Tamsin M. Burland

Seeing in the dark: molecular approaches to the study of bat populations

Whilst the use of molecular genetic techniques is widespread in the fields of population and evolutionary biology, their application within the mammalian order Chiroptera neither reflects the species richness nor the ecological and behavioural diversity of the order. This is despite the fact that the Chiroptera are problematic to study using more direct observational techniques. Here, we standardize and synthesise the current data, assess the contribution of molecular research to the study of bat species and highlight the importance of its continued and expanded use. At an inter‐population level, molecular studies have demonstrated a great diversity of population genetic structure within the order. Among populations of migratory species, genetic structure appears universally low, and hence seasonal movement is likely to be the prevailing influence. However, for sedentary species an array of factors including dispersal ability, extrinsic barriers to gene flow and historical events may determine the extent of genetic partitioning among populations. Intrinsic factors such as wing morphology or roost requirements may also influence population genetic structure in sedentary bat species, a proposal which requires further research. Molecular studies have also made important contributions towards an understanding of social organisation in bats. Evidence indicates that in many polygynous species male mating success does not translate directly into reproductive success, perhaps as a result of multiple mating by females. Estimates of relatedness within and genetic structure among colonies are, in general, very low; a finding which has important implications regarding theories concerning the formation and persistence of bat social groups. Molecular studies have provided new and important insights into the ecology of bats, and have opened up exciting and previously unexplored avenues of research. The data from these studies suggest not only a predictive framework for future studies, but also the use of genetic data in the management and conservation of bat species.

Eusociality in African mole-rats: new insights from patterns of genetic relatedness in the Damaraland mole-rat (Cryptomys damarensis)

After the discovery of eusociality in the naked mole–rat, it was proposed that inbreeding and high colony relatedness in this species were the major underlying factors driving cooperative breeding in African molerats. By contrast, field and laboratory studies of the eusocial Damaraland mole–rat (Cryptomys damarensis) have raised the possibility that this species is an obligate outbreeder, although the build–up of inbreeding over several generations could still occur. Using microsatellite markers, we show that most breeding pairs in wild colonies of the Damaraland mole–rat are indeed unrelated (R = 0.02 ± 0.04) and that mean colony relatedness (R = 0.46 ± 0.01), determined across 15 colonies from three separate populations, is little more than half that previously identified in naked mole–rats. This finding demonstrates that normal familial levels of relatedness are sufficient for the occurrence of eusociality in mammals. Variation in the mean colony relatedness among populations provides support both for the central role played by ecological constraints in cooperative breeding and for the suggestion that inbreeding in naked mole–rats is a response to extreme constraints on dispersal. Approaches that determine the relative importance of an array of extrinsic factors in driving social evolution in African mole–rats are now required.

Colony structure and parentage in wild colonies of co‐operatively breeding Damaraland mole‐rats suggest incest avoidance alone may not maintain reproductive skew

Colonies of co‐operatively breeding African mole‐rats have traditionally been thought to be composed of a single breeding female, one or two breeding males, and their offspring. In the naked mole‐rat (Heterocephalus glaber), the occurrence of facultative inbreeding means incest avoidance cannot prevent reproduction in subordinate group members, and physiological suppression of reproductive function by the breeding female occurs in both sexes. In contrast, previous studies of captive colonies of the Damaraland mole‐rat (Cryptomys damarensis) suggest that breeding within a colony is restricted to a single breeding pair, simply because all other colony members are highly related (first‐ or second‐order relatives) and this species is an obligate outbreeder. Using microsatellite markers, we investigated parentage and colony composition in 18 wild Damaraland mole‐rat colonies to determine whether inbreeding avoidance alone can explain the high levels of reproductive skew in this species. Multiple and unidentified paternity was widespread within colonies and immigrants of both sexes were regularly identified. Unrelated, opposite‐sex nonbreeders were found coexisting in two colonies. These results suggest that, in the wild, conditions exist where nonreproductive females can come into contact with unrelated males, even when they do not disperse from their natal colony. Inbreeding avoidance alone is therefore insufficient to maintain the high levels of reproductive skew identified in this species suggesting that the breeding female somehow suppresses the reproductive function in nonbreeding females.

On the Occlusal Fit of Tribosphenic Molars: Are We Underestimating Species Diversity in the Mesozoic?

The complex occlusal fits between tribosphenic teeth are a rich source of information for taxonomic, phylogenetic, and evolutionary analysis. The degree of fit between upper and lower cheek teeth has been used to refer specimens to species-level taxa, but statistical data on occlusal fit in relation to taxonomic identity have been lacking. We used landmarks on upper and lower first molars of 20 bat populations representing 16 species to assess the degree of occlusal fit (1) between teeth from the same individual; (2) between teeth from different individuals belonging to the same populations; and (3) between teeth belonging to different populations. We found that the fit of teeth belonging to different populations was significantly worse than between those of the same population and that the degree of misfit increased linearly with time since common ancestry, albeit with substantial variance. We used our comparisons to assess the species-level diversity within Batodon, the smallest known placental mammal from the Cretaceous. Our data suggest, with caveats, that instead of belonging to a single species, the specimens assigned to Batodon represent at least two species as different as those belonging to different genera or families of living bats.