Evidence of correlated evolution of hypsodonty and exceptional longevity in endemic insular mammals

Abstract

Here, we test whether the increase in tooth height in insular endemics results from the expansion of the dietary niche under resource limitation, as widely considered, or whether it represents an investment in dental durability in response to the selection for extended longevity under low levels of extrinsic mortality. We tested these hypotheses in the extremely hypsodont fossil bovid Myotragus balearicus from the Balearic Islands, an ideal model to study the evolutionary trends on islands. Dental abrasion was significantly lower in the insular bovid than in highly hypsodont continental artiodactyls, suggesting that feeding habits are not the sole driving force behind increased crown height. However, the estimated longevity for M. balearicus based on dental durability was two times that predicted from body mass. Survivorship curves confirm that an extraordinarily large number of individuals approached the longevity of the species. Our results, hence, provide evidence that hypsodonty in insular endemics is the outcome of selection for increased durability of the permanent dentition in association with an extended lifespan. In the context of insularity, our results lend additional support to the disposable soma theory of ageing confirming the dependency of somatic maintenance and repair on lifespan, and its control by resource availability and extrinsic mortality.

First approach to bone histology and skeletochronology of Equus hemionus

“…Over the last years, several authors have pointed out that the histological study of bones and teeth provides valuable information about the life history strategy of extant and extinct mammals Jordana et al, 2012Jordana et al, , 2014Köhler and Moyà-Solà, 2009;Köhler et al, 2012;Marín-Moratalla et al, 2011, 2013. Our first results from the histology of the femur of E. hemionus support the previous results on mammals and offer a basis for future studies on both extant and extinct equids.…”

Mortality in a Predator-free Insular Environment: the Dwarf Deer of Crete

“…Cervus astylodon evolved increased longevity (Kubo et al, 2011), but not to the extreme degree seen in the dwarf bovid Myotragus balearicus according to Köhler and Solà (2009;Jordana et al, 2012). However, the conclusion of Köhler and Solà (2009) concerning Myotragus was based on the presence of lines of arrested growth (LAG), otherwise exclusive to ectotherms, which they interpreted as due to a periodical, irregular growth rate (a "slow life").…”

Physiological adaptations of ruminants and their potential relevance for production systems

“…Evidently, any characteristic could be chosen as a target for selective breeding. For example, given the variety of dental traits (Archer and Sanson, 2002;Heywood, 2010;Kaiser et al, 2010) and hypsodonty (Mendoza et al, 2002;Damuth and Janis, 2011;Jordana et al, 2012) in ruminants, one could consider breeding domestic ruminants for more complex and higher-crowned teeth, if there was evidence that the production potential of domestic ruminants was constrained by the durability of their teeth. Given the variety of muzzle width (Gordon and Illius, 1988;Janis and Ehrhardt, 1988;Tennant and MacLeod, 2014) in ruminants, one could consider breeding domestic ruminants for wider muzzles to enhance their foraging efficiency, if muzzle width was identified as a constraint.…”