Department of Physics, Chemistry and Biology
Master Thesis
Olfactory discrimination of aliphatic 2-ketones
and 1-alcohols in South African fur seals
(Arctocephalus pusillus pusillus)
Elin Lord
LiTH-IFM- Ex—09/2135--SE
Supervisor: Matthias Laska, Linköpings universitet
Examiner: Per Jensen, Linköpings universitet
Department of Physics, Chemistry and Biology Linköpings universitet
Rapporttyp Report category Licentiatavhandling x Examensarbete C-uppsats x D-uppsats Övrig rapport _______________ Språk Language Svenska/Swedish x Engelska/English ________________ Titel Title:
Olfactory discrimination of aliphatic 2-ketones and 1-alcohols in South African fur seals (Arctocephalus pusillus
pusillus)
Författare
Author: Elin Lord
ISBN
LITH-IFM-A-EX--—09/2135—SE
__________________________________________________ ISRN
__________________________________________________ Serietitel och serienummer ISSN
Title of series, numbering Handledare
Supervisor: Matthias Laska
Ort
Location: Linköping
Nyckelord
Keyword:
Arctocephalus pusillus, Aliphatic ketones, Aliphatic alcohols, Odor discrimination, Olfaction
Datum Date 2009-06-04
URL för elektronisk version
Sammanfattning
Abstract:
Odor discrimination ability was tested in four female South African fur seals (Arctocephalus pusillus pusillus) using a food-rewarded two-choice instrumental conditioning paradigm. The seals’ ability to distinguish between members of homologous series of aliphatic ketones (2-butanone to 2-heptanone) and alcohols (1-butanol to 1-heptanol) was assessed. The results showed that three out of four seals successfully discriminated between all of their stimulus combinations in both classes of odorants. One seal succeeded to reach the discrimination criterion with all 2-ketones but failed with all 1-alcohols.
No significant correlation between odor discrimination performance and structural similarity of the odorants in terms of differences in carbon chain length was found in either of the two chemical classes. Furthermore, it was found that the 2-ketones were significantly better discriminated than the 1-alcohols. The fact that both classes of odorants are known to be present in the natural environment of seals provides a possible explanation as to why most of the seals were able to successfully discriminate between them. The results of the present study support the notion that the sense of smell may play an important role in behavioral contexts such as social communication, foraging and reproductive behavior of fur seals.
Avdelning, Institution Division, Department
Avdelningen för biologi
Contents
1 Abstract ... 1
2 Introduction ... 1
3 Materials and methods ... 2
3.1 Animals ... 2 3.2 Odorants ... 3 3.3 Test procedure ... 3 3.3.1 Experimental set-up ... 4 3.4 Data analysis ... 5 4 Results ... 6 4.1 2-Ketones ... 6 4.2 1-Alcohols ... 6
4.3 Comparison between odorant classes ... 7
5 Discussion ... 8
5.1 2-Ketones ... 8
5.2 1-Alcohols ... 8
5.3 Discrimination as a function of odor similarity ... 9
5.4 Comparison between species ... 9
6 Acknowledgements ... 11
1 1 Abstract
Odor discrimination ability was tested in four female South African fur seals (Arctocephalus pusillus pusillus) using a food-rewarded two-choice instrumental conditioning paradigm. The seals’ ability to distinguish between members of homologous series of aliphatic ketones (2-butanone to 2-heptanone) and alcohols (butanol to 1-heptanol) was assessed. The results showed that three out of four seals successfully discriminated between all of their stimulus combinations in both classes of odorants. One seal succeeded to reach the discrimination criterion with all 2-ketones but failed with all 1-alcohols.
No significant correlation between odor discrimination performance and structural similarity of the odorants in terms of differences in carbon chain length was found in either of the two chemical classes. Furthermore, it was found that the 2-ketones were significantly better discriminated than the 1-alcohols. The fact that both classes of odorants are known to be present in the natural environment of seals provides a possible explanation as to why most of the seals were able to successfully discriminate between them. The results of the present study support the notion that the sense of smell may play an important role in behavioral contexts such as social communication, foraging and reproductive behavior of fur seals.
Keywords: Arctocephalus pusillus, Aliphatic ketones, Aliphatic alcohols, Odor discrimination, Olfaction
2 Introduction
Marine mammals are traditionally considered to have a poor sense of smell. This view is mainly based on an interpretation of anatomical evidence and not on behavioral or physiological studies (Fobes & Smock 1981). More recent studies suggest that olfaction may indeed play an important role for social communication, foraging and reproductive behavior in many pinnipeds, including fur seals. Burton et al. (1975) observed postnatal smelling of the pup by the mother to establish identity in grey seals (Halichoerus grypus). The use of olfaction for mother-pup recognition has also been reported in Alaska fur seals, Callorhinus ursinus (Bartholomew 1959), harp seals, Phoca groenlandica (Kovacs 1987, Kovacs 1995), Antarctic fur seals, Arctocephalus gazelle (Dobson & Jouventin 2003) and South American fur seals, Arctocephalus australis (Phillips 2003). Ross (1972) observed nose-to-nose nuzzling in captive South African fur seals. There have also been observations of adult male New Zealand fur seals (Arctocephalus forsteri) smelling the perineal and facial regions of females (Miller 1974).
Only few studies so far assessed olfactory performance in pinnipeds. Kowalewsky et al. (2006) reported that harbor seals (Phoca vitulina vitulina) have a well-developed olfactory sensitivity for dimethyl sulphide (DMS) which is often present in areas of high marine productivity and where it is likely to find prey (Thomas & Miller 1990). Laska et al. (2008) showed that South African fur seals (Arctocephalus pusillus pusillus) can discriminate between fish- and non-fish odors as well as between two fish odors which supports the notion that fur seals may use olfactory cues for social communication and foraging. Selin (2008) tested the same species on olfactory discrimination of carboxylic acids, aliphatic aldehydes and acetic esters. Carboxylic acids and aliphatic aldehydes are odor classes that are widespread in the natural environment of pinnipeds. Acetic esters
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are rather rare in the marine environment and are typically present in odors of fruit (Alasalvar et al. 1997). It was found that seals can successfully discriminate between members of these odor classes although two seals failed to discriminate between one pair of acetic esters. These results too support the notion that fur seals may use olfactory cues for social communication, foraging and reproductive behavior.
The present study is intended to continue on the same path as Laska et al. (2008) and Selin (2008) and assess olfactory discrimination abilities of South African fur seals for odor classes that may be relevant for foraging and social communication of seals. 2-ketones have been reported to be present in a variety of fish and seafood odors (Olafsdottir et al. 2005, Burdock 2005) and also in seal blubber oil (Cadwallader & Shahidi 2001). 1-alcohols have also been reported to be components in a wide variety of fish and seafood odors (Burdock 2005, Josephson et al. 1991). Both these odor classes may thus be behaviorally relevant in foraging and social communication in seals.
The use of structurally related odorants allows me to additionally assess whether there is a correlation between olfactory discrimination performance of the seals and structural similarities of the odorants in terms of differences in carbon chain length.
The aims of the present study is threefold: (i) to assess the olfactory discrimination ability of South African fur seals for homologous series of 2-ketones and 1-alcohols; (ii) to assess a potential correlation between olfactory discrimination performance and structural similarity of odorants in terms of differences in carbon chain length; and (iii) by comparing the results from the present study to those of earlier studies done on both the same classes of odorants and on South African fur seals to assess differences and similarities in odor discrimination performance between species and between odorant classes.
3 Materials and methods 3.1 Animals
The study was conducted using four adult female South African fur seals (Arctocephalus pusillus pusillus) kept as part of a group of nine animals at Kolmården Wild Animal Park, Sweden. The group was housed under semi-natural conditions in an 800 m2 outdoor pool neighbouring a house bearing single cages. The four animals (Flisa, Tinny, Sealia and Villma) were trained to enter the cages voluntarily and were fully accustomed to the procedure which allowed temporary separation for individual testing. One of the females used in the experiments (Flisa) was kept in the same cage as her 5 month old cub. Feeding of fish and occasionally squid occurred twice a day.
The experiments reported here comply with the Guide for the Care and Use of Laboratory Animals (National Institutes of Health Publication no. 86-23, revised 1985) and also with current Swedish laws.
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Figure 1. The South African fur seal (Arctocephalus pusillus pusillus), Villma. (photo by Therése Höglin).
3.2 Odorants
A total of 9 odorants, including two sets of four structurally related odorants (Table 1) and the essential oil of black pepper (Piper nigrum) were used. The sets of odorants included members of two chemical classes: aliphatic 2-ketones and 1-alcohols, which only differed from each other in carbon chain length (C4-C7). All odorants, with the exception of the essential oil, were diluted using odorless diethyl phthalate as the solvent. The level of dilution for each of the odorants was chosen to provide stimuli that were easily detectable and of approximately equal subjective intensity for humans.
Table 1. Substances and dilutions
2-ketones Dilution 1-alcohols Dilution
2-butanone (C4) 1:10 1-butanol (C4) 1:10
2-pentanone (C5) 1:10 1-pentanol (C5) 1:10
2-hexanone (C6) 1:3 1-hexanol (C6) 1:3
2-heptanone (C7) 1:3 1-heptanol (C7) 1:3
3.3 Test procedure
The test was based on a food-rewarded two-choice instrumental conditioning paradigm (Laska et al. 2008a). In a previous study, the animals had been trained to sniff at two odor sampling ports and then to indicate their choice for one of the options by poking their nose into the corresponding sampling port.
For each of the two sets of stimuli, one odorant (either the C4 or the C7 stimulus) per animal was chosen as the rewarded stimulus (S+) and in an initial phase, each animal was allowed to become familiar with its S+. This was done by using black pepper oil as
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unrewarded stimulus (S-) in up to ten sessions. Black pepper oil had been used as S- in previous experiments and was therefore known to the animals. Once familiarized with the S+, the black pepper oil was exchanged for one of the other odorants of the same set (Table 2) and each of the critical stimulus combinations was presented for four sessions. If needed, up to two sessions with black pepper oil as S- were implemented between the different test combinations in order to boost the animal’s confidence and to refresh its memory for the reward value of the S+.
Table 2. Assignment of odor pairs to groups according to differences in carbon chain length. ∆C1 corresponds to the discrimination of odorants which differ by only one carbon atom, and ∆C2 and ∆C3 to the discrimination of odorants which differ by two and three carbon atoms, respectively.
∆C1 ∆C2 ∆C3
4-5 4-6 4-7
6-7 5-7
3.3.1Experimental set-up
An opaque PVC board (50 x 100 x 1 cm) with two openings was placed at the front of the test cage. The two openings (7.5 cm diameter) were positioned 42 cm apart, at the same height and, with the board mounted onto the front side of the cage, 47 cm above the ground. Five HDPE containers (Rubbermaid® Cooling Bags, 35 x 35 x 20 cm) were used to present the odor stimuli – one for the S- (black pepper oil) and one each for the four stimuli of a given set of odorants (see Table 1). On the front side of the containers, a total of 130 holes (3 mm diameter) were drilled, distributed in intervals of even distance making it a filled circle (7.5 cm diameter) matching the openings on the PVC board. The removable lids were tight-fitted and two of them were equipped with a battery-powered ventilator (6 cm diameter) with the purpose of providing a constant airflow through the container and creating an outflow of 8 L/min at the holes on the front. In order to present the odor stimuli without giving the animals any visual cues, 1 ml of the odorant was pipetted onto a Petri dish which in turn was placed into an opaque HDPE box (12 x 20 x 12 cm) which then was put in the container. A mirror placed on the top of the cage allowed the experimenter to observe the animal’s behavior behind the opaque board without being seen and without giving any unintentional visual cues.
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At the beginning of each trial, the two containers were placed with their outlets towards the odor sampling ports. The animal was then allowed to sniff at both ports as long and as often as it needed to make a choice. Immediately after an animal had indicated its choice by poking its nose into the corresponding odor port, the containers were removed. In case of a correct choice, the animal received fish or squid as a reward, in case of an incorrect choice, a new trial began after a short time-out without any reward. Twenty such trials were performed per session and usually two sessions were carried out per day and animal. The order in which the rewarded stimulus was presented to the right or left odor sampling port followed a pseudorandomized sequence with the limitation that the same side was not used more than three times in a row. At the end of each session, the containers and the boxes that had been used were thoroughly cleaned.
3.4 Data analysis
In each trial, two outcomes were possible: (1) a correct response to the rewarded stimulus (hit), and (2) a false response to the negative stimulus (false alarm). The percentage of correct decisions was used as the measure of performance and the criterion was set to 67.5% correct in two consecutive sessions of 20 decisions each, which means 27 out of 40 trials (corresponding to p < 0.05, two-tailed binomial test).
Correlations between discrimination performance and structural similarity of odorants in terms of differences in carbon chain length were evaluated using the Spearman rank correlation coefficient.
Figure 2. Left: Schematic drawing of the experimental set-up used to assess olfactory performance in South African fur seals. C: container; V: ventilator for ingoing airflow; SB: stimulus box; O: outlet for outgoing airflow; OP1: odor port 1; OP2: odor port 2. The second, identically built container placed behind odor port 2, is not shown. Right: Photo of the experimental set-up used to assess olfactory performance in South African fur seals. OP1: odor port 1; OP2: odor port 2. The containers cannot be seen in the picture.
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Comparisons of group performance between the two chemical classes were made using the Wilcoxon signed-rank test.
Comparisons of group performance between the two chemical classes and three chemical classes used in a previous study were made using the Wilcoxon signed-rank test.
4 Results 4.1 2-Ketones
Figure 1 illustrates the performance of the four fur seals in discriminating between different odor pairs of aliphatic 2-ketones. All four animals tested reached the criterion with all odor pairs. They could thus clearly discriminate between the different 2-ketones used.
No statistically significant correlation between discrimination performance and structural similarity in terms of difference in carbon chain length was found (Spearman, rs=0.045;
p=0.89). Accordingly, only one of the animals (Sealia) showed a decrease in performance that followed a decrease in structural similarity in terms of difference in carbon chain length.
Figure 3. Performance of the four fur seals in discriminating between members of a homologous series of 2-ketones. Each data point represents the percentage of correct choices from 40 consecutive trials. The different symbols represent individual data from the four animals tested.
4.2 1-Alcohols
Figure 2 illustrates the performance of the four fur seals in discriminating between different odor pairs of aliphatic 1-alcohols. Three animals reached the criterion with all
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odor pairs and could thus clearly discriminate between the different 1-alcohols used. One animal (Sealia) did not reach the criterion for any odor pair.
No statistically significant correlation between discrimination performance and structural similarity in terms of differences in carbon chain length was found (Spearman, rs=0.239;
p=0.454). Two of the animals (Flisa and Tinny) showed an increase in performance whilst one animal (Sealia) showed a decrease in performance that followed a decrease in structural similarity in terms of differences in carbon chain length.
Figure 4. Performance of the four fur seals in discriminating between members of a homologous series of 1-alcohols. Each data point represents the percentage of correct choices from 40 consecutive trials. The different symbols represent individual data from the four animals tested. The black triangles represents the odor pairs that the fur seals did not discriminate significantly above chance level (binomial test, p>0.05).
4.3 Comparison between odorant classes
A statistical comparison of performance between the two chemical classes showed that the 2-ketones were significantly better discriminated than the 1-alcohols (Wilcoxon, z=-2.284; p=0.022). This is also illustrated by a comparison of the average performance (mean ± SE) across all odor pairs within a given class. Whereas the percentage of correct discriminations was 79.4±2.5% with the 2-ketones, it was only 72.5±2.9% with the 1-alcohols.
The 1-alcohols were also the one chemical class, out of the two, in which an animal failed to reach the criterion for discrimination with all of the stimulus combinations.
8 5 Discussion
The present study shows that South African fur seals are able to discriminate odors belonging to the chemical classes of 2-ketones and 1-alcohols. No significant correlation between odor discrimination performance and structural similarity in terms of differences in carbon chain length in either odor class was found. The 2-ketones were found to be significantly better discriminated than the 1-alcohols.
5.1 2-Ketones
South African fur seals include a variety of fish in their diet and also cephalopods and crustaceans. The odor of fish is complex and is composed of substances from a variety of chemical classes. Ketones are one chemical class that contributes to fish odor (Alasalvar et al. 1997). Ketones have been found in the odors of a variety of marine animals. They have been reported in seal blubber oil (Cadwallader & Shahidi 2001), dry squid, Loligo edulis edulis (Kawai et al. 1991) and in fresh mackerel, Scomber scombrus (Alasalvar et al. 1997). According to Alasalvar the proportion of ketones was higher in fresh mackerel than that of aldehydes and esters (ketones 13.65%; aldehydes 8.66%; esters 8.27%). Ketones have also been found in snowcrab, Chionoecetes opilio (Cha et al. 1993). Olafsdottir et al. (2005) found 2-butanone in cod fillets (Gadus morhua) during spoilage. 2-pentanone can be found in shrimp and crab and 2-heptanone in shrimp, oysters, crab and crayfish (Burdock 2005). Girard and Durance (2000) reported that 2-butanone is present in high concentrations in both sockeye salmon (Oncorhynchus nerka) and pink salmon (Oncorhynchus gorbuscha).
The fact that ketones are widespread in the odors of the seal’s diet might plausibly explain why they were able to discriminate them at the level that they did.
Results from previous studies suggest that seals may use olfaction for foraging (Kowalewsky et al. 2006, Selin 2008). As ketones are widespread in the diet of seals, it is thus possible that this group of odors play a role in foraging.
5.2 1-Alcohols
Alcohols have also been reported to be present in the odor of seafood. As a group, short-chain alcohols might contribute to odors characterizing fresh or nearly fresh fish (Alasalvar et al. 1997).
1-butanol, 1-pentanol, 1-hexanol and 1-heptanol have all been found in small concentrations in both sockeye, Oncorhynchus nerka, and pink salmon, Oncorhynchus gorbuscha (Girard & Durance 2000).
1-hexanol is present in kelp and 1-heptanol in crab, crayfish and clams (Burdock 2005). Josephson et al. (1991) found 1-pentanol, 1-hexanol and 1-heptanol in spawning-condition, freshwater Pacific Ocean salmon (Oncorhynchus kisutch). 1-butanol was reported in the skin of Horse mackerel (Trachurus japonicus) and Pacific mackerel (Scomber melanostica) and in both muscle and skin of sardine (Sardinops melanostica) (Mansur et al. 2003). Mansur et al. also reported about 1-pentanol and 1-hexanol in the skin of Pacific mackerel and 1-pentanol was found in skin and muscle of Red sea bream (Pagrus major) and hexanol in skin of sardine. Zhang and Lee (1997) also found 1-hexanol in mackerel.
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According to Ganeko et al. (2008), 1-hexanol and 1-heptanol are present in fresh sardines. Alcohols, in general, appear to be present in a wide variety of seafood (Josephson 1991) but usually only at low concentrations (Laska & Teubner 1999).
The majority of a South African fur seal’s diet consists of sardines and mackerel (King 1983, Seal Conservation Society 2001). As all the 1-alcohols used in the present study are present in either or both sardines and mackerel, it seems plausible that fur seals have a good ability to discriminate them and may use them as olfactory cues to find prey.
5.3 Discrimination as a function of odor similarity
Several studies assessed the relationship between discrimination performance and similarity in carbon chain length of odorants in species other than fur seals. A statistically significant negative correlation between discrimination performance and similarity in carbon chain length of 2-ketones has been found in humans (Laska & Hübener 2001), squirrel monkeys, Saimiri sicureus (Laska et al. 1999a), bees, Apis mellifera carnica (Laska et al. 1999b) and mice, Mus musculus (Laska et al. 2008b). Similarly, a significant negative correlation between discrimination performance and similarity in carbon chain length of 1-alcohols has been reported in humans (Laska & Teubner 1999), squirrel monkeys (Laska et al. 1999a), spider monkeys, Ateles geoffroyi (Laska et al. 2006) and bees (Laska et al. 1999b). However, no such correlation was found with 1-alcohols in mice (Laska et al. 2008b).
In the present study, no such significant correlation was found neither with the 1-alcohols nor the 2-ketones which is somewhat surprising as this differs from most of previous studies.
The negative correlation found in most other studies is in agreement with electrophysiological findings that showed that tuning specificities of rodent olfactory receptor neurons correlate with carbon chain length of, amongst others, aliphatic alcohols. The fact that no correlation was found with 1-alcohols in mice suggests that correlations found at the neurophysiological level do not have to be predictive of discrimination performance at the behavioral level. This might be the case in the present study as well. More studies are needed on other species and more assessments on possible correlations between discrimination performance and carbon chain length should be performed.
5.4 Comparison between species
Previous studies on olfactory discrimination with 2-ketones and 1-alcohols in humans, squirrel monkeys and bees, allow for a direct comparison of performance with that of the fur seals tested here.
Humans failed to significantly discriminate between 2-ketones with three out of 21 tasks (Laska & Hübener 2001). For example, they failed to discriminate between 2-butanone and 2-pentanone which both seals could successfully discriminate. Laska and Hübener (2001) showed that it was significantly more difficult for the humans to discriminate all odor pairs that differed by only one carbon than those that differed by three to six carbons and some of the odor pairs that differed by two carbons. This was not seen in the present study.
When comparing the olfactory discrimination of bees and seals, the bees, as a group, failed to significantly discriminate between 2-ketones with three out of 49 tasks. For
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example, they failed to discriminate between 2-hexanone and 2-heptanone which both seals successfully discriminated.
There are differences worth noting between performance in humans and fur seals when discriminating between 1-alcohols. Humans failed to significantly discriminate between 1-alcohols with two out of 21 tasks (Laska & Teubner 1999). One was 1-hexanol versus 1-heptanol which was successfully discriminated by the seals. One seal out of two failed to significantly discriminate between 1-pentanol and 1-heptanol which were successfully discriminated by humans.
In another study, humans, as a group, failed to significantly discriminate between alcohols with two out of six tasks (Laska et al. 1999). One was pentanol versus 1-butanol which both seals successfully discriminated. In the same study, squirrel monkeys, as a group, also failed to significantly discriminate between 1-pentanol and 1-butanol.
5.5 Comparison with results from Selin, 2008
Only few studies assessed olfactory discrimination capabilities in South African fur seals so far. Using the same apparatus and experimental design as in the present study, Selin (2008) tested five seals on olfactory discrimination of carboxylic acids, aliphatic aldehydes and acetic esters.
A statistical comparison of performance between the results from that study and the present study shows that the seals were significantly better at discriminating aliphatic aldehydes than alcohols (Wilcoxon, z=-2.127; p=0.033). This was further supported when looking at average performance (mean ± SE) for these two odor classes (aldehydes: 84.77±3.07%; alcohols: 72.5±2.92%). These two odor classes showed the largest difference in mean performance amongst the five. Aliphatic aldehydes are very common in the natural environment of seals (Alasalvar et al. 1997), so it should therefore be expected that the seals have a very good ability to discriminate this class of odors. The seals were not significantly better or poorer at discriminating any of the other classes.
5.6 Olfaction in seals
Based on anatomical evidence marine mammals are often considered to have a poor sense of smell (Fobes & Smock 1981). Pinnipeds are considered to have reduced olfactory areas compared to terrestrial mammals, but they are not entirely lacking such areas (Lowell & Flanigan 1980). MacKay-Sim et al. (1985) reported that all species of pinnipeds have olfactory and accessory olfactory systems including the vomeronasal organ. According to Kuzin and Sobolevsky (1976 as cited by Lowell & Flanigan 1980) the olfactory epithelium of the fur seal is typically mammalian which should indicate that they have a well developed sense of smell.
Several studies suggest that seals may use olfaction in their social behavior. Burton et al. (1975) observed births and postnatal behavior in grey seals (Halichoerus grypus) and found that immediately after parturition, the mother turned to smell the pup. The smelling continued especially during the first ten minutes after parturition. The mother also smelled the placenta. This is thought to enable the cow to establish the identity of its pup. A common behavior seen in seals is the use of olfaction for recognition of the pup by the mother after she has been out foraging at sea. Bartholomew (1959) was one of the first to describe this behavior in wild Alaska fur seals (Callorhinus ursinus). After vocalizations from the female, pups approached and she smelled at their noses. If the pup was not her
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own she either ignored it or showed aggressive behavior towards it until it shunned. If the pup was hers, she stood still and quiet while the pup moved to the side, looking for a nipple. The same behavior has been observed in other studies and species of seals as well (Harp seal, Phoca groenlandica: Kovacs 1987, Kovacs 1995; Antarctic fur seal, Arctocephalus gazella: Dobson & Jouventin 2003; South American fur seal, Arctocephalus australis: Phillips 2003). This strongly suggests that olfaction is important as a tool for maternal recognition of pups.
Miller (1974) reported that adult male New Zealand fur seals (Arctocephalus forsteri) frequently attempted and succeeded to smell at the perineal and facial regions of females. It seemed that olfactory investigation was the only means by which males regularly could assess the reproductive states of females before copulation.
Kowalewsky et al. (2006) found that harbor seals (Phoca vitulina vitulina) have a very high olfactory sensitivity for dimethyl sulphide (DMS) which are often found in offshore sandbanks and rocky reefs from production by plankton (Steinke 2006). Offshore sandbanks and rocky reefs have been observed to be a regular foraging site for harbor seals (Thompson & Miller 1990).
These observations show how behaviorally important olfaction can be for seals. The fur seals in the present study were successful in discriminating the odorants used here. Combining the information that these odorants are all present in the natural environment of seals, foremost in their diet and that olfaction can be important for seals, suggests that fur seals may use 2-ketones and 1-alcohols as olfactory cues for prey.
5.7 Conclusion
The present study provides evidence that South African fur seals have a well-developed ability to discriminate between monomolecular odorants belonging to the classes of 2-ketones and 1-alcohols.
Ketones and alcohols are present in the odors of a wide variety of marine animals that are part of the diet of South African fur seals. This might be a plausible explanation why the seals in the present study were able to successfully discriminate between most odor pairs. Further studies should assess discrimination performance for other odor classes both with and without behavioral relevance for the seals to increase knowledge about olfactory performance in seals and its role in social communication, foraging and reproductive behavior.
6 Acknowledgements
I would like to thank my supervisor Professor Matthias Laska for his help and patience during this study. I would especially like to thank Sunna Edberg and Therése Höglin for teaching me how to do the data collection. Without the trainees from Himmelstalunds agricultural high school and all the caretakers at the dolphinarium at Kolmården Wild Animal Park, this study would have been impossible to perform. Finally, I would like to thank Mats Amundin for the help during my time in Kolmården.
7 References
Alasalvar C, Quantick PC & Grigor JM (1997) Aroma compounds of fresh and stored mackerel (Scomber scombrus) in: Shahidi F & Cadwallader KR (eds) Flavor and lipid chemistry of seafoods. pp 39-54. ACS Symp Series, 674. Washington, DC.
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Burdock GA (2005) Fenaroli’s handbook of flavor ingredients. 5th ed. CRC Press, London.
Burton RW, Anderson SS & Summers CF (1975) Perinatal activities in the grey seal (Halichoerus grypus). Journal of Zoology 177, 197-201.
Cha YJ, Cadwallader KR & Baek HH (1993) Volatile flavor components in snow crab cooker effluent and effluent concentrate. Journal of Food Science 58, 525-530.
Dobson FS & Jouventin P (2003) How mothers find their pups in a colony of Antarctic fur seals. Behavioural Processes 61, 77-85.
Fobes JL & Smock CC (1981) Sensory capacities of marine mammals. Psychological Bulletin 89, 288-307.
Ganeko N, Shoda M, Hirohara I, Bhadra A, Ishida T, Matsuda H, Takamura H & Matoba T (2008) Analysis of volatile flavor compounds of sardine (Sardinops melanostica) by solid phase microextraction. Journal of Food Science 73, 83-88.
Girard B & Durance T (2000) Headspace volatiles of sockeye and pink salmon as affected by retort process. Journal of Food Science 65, 34-39.
Josephson DB (1991) Seafood in: Maarse H (ed) Volatile compounds in foods and beverages. pp 179-202. Marcel Dekker, New York.
Josephson DB, Lindsay RC & Stuiber DA (1991) Influence of maturity on the volatile aroma compounds from fresh pacific and Great Lakes salmon. Journal of Food Science 56, 1576-1579.
Kawai T, Ishida Y, Kakiuchi H, Ikeda N, Higashida T & Nakamura S (1991) Flavor components of dried squid. Journal of Agricultural and Food Chemistry 39, 770-777.
King JE (1983) Seals of the world. 2nd ed. Oxford University Press, Oxford.
Kovacs KM (1987) Maternal behaviour and early behavioural ontogeny of harp seals, Phoca groenlandica. Animal Behaviour 35, 844-855.
Kovacs KM (1995) Mother-pup reunions in harp seals, Phoca groenlandica: cues for the relocation of pups. Canadian Journal of Zoology 73, 843-849.
Kowalewsky S, Dambach M, Mauck, B & Dehnhardt G (2006) High olfactory sensitivity for dimethyl sulphide in harbour seals. Biology Letters 2, 106-109.
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Kuzin AY & Sobolevsky YI (1976) Morphological and functional characteristics of the fur seal’s respiratory system. Proceedings of the 6th All-Union Conference on the Study of Marine Mammals, Kiev. Joint Publishing Service. Arlington, Virginia.
Laska M, Galizia CG, Giurfa M & Menzel R (1999b) Olfactory discrimination ability and odor structure-activity relationships in honeybees. Chemical Senses 24, 429-438.
Laska M & Hübener F (2001) Olfactory discrimination ability for homologous series of aliphatic ketones and acetic esters. Behavioural Brain Research 119, 193-201.
Laska M, Rivas Bautista RM & Hernandez Salazar LT (2006) Olfactory sensitivity for aliphatic alcohols and aldehydes in spider monkeys (Ateles geoffroyi). American Journal of Physical Anthropology 129, 112-120.
Laska M, Rosandher Å & Hommen S (2008b) Olfactory discrimination of aliphatic odorants at 1 ppm: too easy for CD-1 mice to show odor structure-activity relationships? Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology 194, 971-980.
Laska M, Svelander M & Amundin M (2008a) Successful acquisition of an olfactory discrimination paradigm by South African fur seals, Arctocephalus pusillus. Physiology & Behavior 93, 1033-1038.
Laska M & Teubner P (1999) Olfactory discrimination ability for homologous series of aliphatic alcohols and aldehydes. Chemical Senses 24, 263-270.
Laska M, Trolp S & Teubner P (1999a) Odor structure-activity relationships compared in human and nonhuman primates. Behavioral Neuroscience 113, 998-1007.
Lowell WR & Flanigan Jr WF (1980) Marine mammal chemoreception. Mammal Review 10, 53-59.
MacKay-Sim A, Duvall D & Graves BM (1985) The West Indian manatee Trichechus manatus, lacks a vomeronasal organ. Brain, Behavior amd Evolution 27, 186-194.
Mansur MA, Bhadra A, Takamura H & Matoba T (2003) Volatile flavor compounds of some sea fish and prawn species. Fisheries Science 69, 864-866.
Miller EH (1974) Social behaviour between adult male and female New Zealand fur seals, Arctocephalus forsteri (Lesson) during the breeding season. Australian Journal of Zoology 22, 155-173.
Olafsdottir G, Jonsdottir R, Lauzin HL, Luten J & Kristbergsson K (2005) Characterization of volatile compounds in chilled cod (Gadus morhua) fillets by gas chromatography and detection of quality indicators by an electronic nose. Journal of Agricultural and Food Chemistry 53, 10140-10147.
14
Phillips AV (2003) Behavioral cues used in reunions between mother and pup South American fur seals (Arctocephalus australis). Journal of Mammalogy 84, 524-535.
Ross GJB (1972) Nuzzling behaviour in captive Cape fur seals Arctocephalus pusillus. International Zoo Yearbook 12, 183-184.
Seal Conservation Society (2001) South African and Australian fur seals (Arctocephalus pusillus) www.pinnipeds.org/species/saausfur.htm (3 march 2009).
Selin S (2008) Olfactory discrimination of aliphatic aldehydes, carboxylic acids and acetic esters in South African fur seals (Arctocephalus pusillus). M.Sc. Thesis, Linköping University.
Steinke M (2006) Ocean odours. Planet Earth WINTER, 16-17.
Thompson PM & Miller D (1990) Summer foraging activity and movements of radio-tagged common seals (Phoca vitulina. L.) in the Moray Firth, Scotland. Journal of Applied Ecology 27, 492-501.
Zhang H-Z & Lee T-C (1997) Gas chromatography-mass spectrometry analysis of volatile flavor compounds in mackerel for assessment of fish quality pp 55-63 in: Shahidi F & Cadwallader KR (eds) Flavor and lipid chemistry of seafoods. ACS Symp Series, 674. Washington, DC.
