A hierarchical cluster analysis was performed on the scent data from the spraints and anal jellies collected in Monmouthshire (Figure 6.2) and although some spraints which were from similar geographical locations clustered in scent (e.g. 19 and 23), many did not (samples are identified in the cluster analysis with a number, the geographical location of these are shown in Figure 6.3). Furthermore some samples grouped in the cluster analysis which were unlikely to be from the same otter due to lack of connected water courses (e.g. 4 and 13). There was no correlation between the spatial distance matrix and the scent distance matrix (r=0.10, n=25, p=0.13).
99 Figure 6.2. Hierarchical cluster analysis of volatile compounds from otter spraints and anal jelly collected on the same day in Monmouthshire. Samples were analysed using solid phase microextraction and gas chromatography mass spectrometry.
Numbers indicate sample number and the geographical locations of samples are shown in Figure 6.3.
Figure 6.3. Location of spraint or anal jelly found on the River Wye and Gwent levels in May 2010. Filled circles are sites where samples were found, open circles are sites where no otter signs were found.
100
6.4. Discussion
Significant differences in the anal gland scent of otters were found between the four genetic subpopulations in the UK, indicating that scent signals are differentiated at a regional scale. These four genetic subpopulations are the result of the UK otter
population decline in the last century, and recovery from small and spatially separated surviving populations (Hobbs et al., 2011). This finding is in agreement with the
growing body of evidence of scent similarity and genetic similarity mostly derived from studies of relatedness at an individual level (Sun and Müller-Schwarze, 1998b;
Charpentier et al., 2008; Boulet et al., 2009). Although an association between genetic similarity and scent similarity has been found between bat colonies, the authors did not find the same association within colonies (Safi and Kerth, 2003). These scent
differences are more likely to reflect colony membership rather than genetic similarity.
The present results appear to be the first evidence of genetic and scent similarity in any species at the population genetics level. Additionally most studies in this field of research are on captive populations; this Chapter is one of very few studies on free-ranging wild populations.
Differences in rabbit odours have been found based on geographical distance (Hayes et al., 2002). For otters, however, the present indicate that geographical distance alone is not a good measure of difference in scent as there was no correlation between
geographical distance and scent distance. An otter’s scent is associated with its location but only in terms of the genetic subpopulation it belongs to. Some geographical
distances between otter locations may not be relevant to relatedness, for example there may be a very short distance between otters but a migration barrier such as a large road prevents breeding between them.
Other research has not found an association between relatedness and VOCs, for example in spotted hyenas (Burgener et al., 2009) and North American river otters are reported to not discriminate between scents depending on the relatedness of the donor conspecific (Rostain et al., 2004). Both these studies only tested a single sex. The present results indicate that the genetic differences are expressed in scent differently between males and females. There was a significant interaction between genetic
101 subpopulations and sex; differences between the genetic subpopulations were
significant for females and near significant for male otters. Similar to other variables tested in other Chapters, only a small amount of variation in the scent was explained by the genetic sub populations. It is possible that variation caused by other variables prevented Burgener et al. (2009) from finding differences in scent associated with relatedness. Alternatively, the results presented here for female otters may be clearer than for male otters due to the larger number of females (n=77) than males (n=46) in the dataset. Burgener et al. had a smaller sample size for their tests (although the total sample size was 50, this consisted of three clans which were analysed separately).
On a small scale (within Monmouthshire) there was no correlation between spraint location and scent. Although differences in spraint scent between individual otters were found in Chapter 5, the resolution of these differences was not strong enough to make predictions from unknown spraints collected in the wild. It is not surprising that clear differences based on location and scent were not found. Those samples that are similar in scent and location are likely to be from the same otter but it is not possible to confirm this. Similarities in scent between samples which are thought to be geographically separated due to lack of connected water courses are likely to be from different otters but of the same age or sex group. Samples which are close in location but very different in scent may indicate overlapping territories as has been found through genetic analysis of otter spraint (e.g. Kalz et al., 2006) or the marking of territory edges. Future research should incorporate genetic analysis of spraint, in order to independently verify scent differences. Additionally, genetic analysis of tissues and scent analysis from glands originating from the same animals could be used to further test the hypothesis that scent differences are associated with relatedness.
In summary, it is not possible to use scent profiles and geographical location of spraint samples to infer individual otter identity. The main finding of this study is that genetic subpopulations of Lutra lutra differ in the odour profiles of their anal gland secretions.
102