Skull variation in Afro-Eurasian monkeys results from both adaptive and non-adaptive evolutionary processes

Abstract

Afro-Eurasian monkeys originated in the Miocene and are the most species-rich modern primate family. Molecular and fossil data have provided considerable insight into their evolutionary divergence, but we know considerably less about the evolutionary processes that underlie these differences. Here, we apply tests developed from quantitative genetics theory to a large (n > 3000) cranio-mandibular morphometric dataset, investigating the relative importance of adaptation (natural selection) and neutral processes (genetic drift) in shaping diversity at different taxonomic levels, an approach applied previously to monkeys of the Americas, apes, hominins, and other vertebrate taxa. Results indicate that natural selection, particularly for differences in size, plays a significant role in diversifying Afro-Eurasian monkeys as a whole. However, drift appears to better explain skull divergence within the subfamily Colobinae, and in particular the African colobine clade, likely due to habitat fragmentation. Small and declining population sizes make it likely that drift will continue in this taxon, with potentially dire implications for genetic diversity and future resilience in the face of environmental change. For the other taxa, many of whom also have decreasing populations and are threatened, understanding adaptive pressures similarly helps identify relative vulnerability and may assist with prioritising scarce conservation resources.

Using developmental rules to align microevolution with macroevolution

“…For more complex structures formed by the interaction of multiple tissues, it might be harder to devise simple models that sufficiently describe the system ontogeny and variation. However, works that focus on the mammalian skull, and that used individualized bone measurements have had a good track-record of modeling multivariate evolution of these structures under microevolutionary models 12,21,55,77,78 , going even further than the simple alignment between variation and evolutionary rates 8,49,55 history, measuring them individually might represent a good first approximation of the multiple morphogenic fields that interact to form the complete structure. This perspective contrasts with the regular practice of constructing morphospaces as comprehensive, phenomenological, and statistical descriptors of biological form without a clear connection to underlying biological processes 18,35,79,80 .…”

Addressing the growing fossil record of subadult hominins by reaching across disciplines

“…The collated submissions were uploaded to a common web drive the month before the workshop. 3,6,12,[37][38][39][40][41][42][43][44][45][46][47][48][49] The first evening of the workshop was an informal meet and greet of our participants, as many did not know each other.…”

“…Before the workshop, participants were asked to provide to the group one paper that best described the participant's interest or approach to the topic, and two papers that were less specific but that would contribute to the foundation for the workshop discussions. The collated submissions were uploaded to a common web drive the month before the workshop 3,6,12,37–49 …”