The Biology of Speciation

Abstract

"Ecological speciation" is defined as the case in which divergent selection leads to reproductive isolation, with speciation under uniform selection, polyploid speciation, and speciation by genetic drift defined as "nonecological." We review these proposed cases of nonecological speciation and conclude that speciation by uniform selection and polyploidy normally involve ecological processes. Furthermore, because selection can impart reproductive isolation both directly through traits under selection and indirectly through pleiotropy and linkage, it is much more effective in producing isolation than genetic drift. We thus argue that natural selection is a ubiquitous part of speciation, and given the many ways in which stochastic and deterministic factors may interact during divergence, we question whether the ecological speciation concept is useful. We also suggest that geographic isolation caused by adaptation to different habitats plays a major, and largely neglected, role in speciation. We thus provide a framework for incorporating geographic isolation into the biological species concept (BSC) by separating ecological from historical processes that govern species distributions, allowing for an estimate of geographic isolation based upon genetic differences between taxa. Finally, we suggest that the individual and relative contributions of all potential barriers be estimated for species pairs that have recently achieved species status under the criteria of the BSC. Only in this way will it be possible to distinguish those barriers that have actually contributed to speciation from those that have accumulated after speciation is complete. We conclude that ecological adaptation is the major driver of reproductive isolation, and that the term "biology of speciation," as proposed by Mayr, remains an accurate and useful characterization of the diversity of speciation mechanisms.

Extraordinarily rapid life-history divergence between Cryptasterina sea star species

“…Such 'ecological speciation' events are increasingly acknowledged as an important source of biological diversity at the species level [8 -13]. However, in the absence of experimental evidence [14,15] for some specific ecological selective agent(s), there can be uncertainty about the contribution of other factors to divergence and speciation [16,17]. In particular, ecological differences between broadly distributed species that diverged long ago could have arisen in many places at any time after their divergence, and could be a consequence (e.g.…”

Community assembly in Lake Tanganyika cichlid fish: quantifying the contributions of both niche‐based and neutral processes

“…This may lead to an increase in the importance of limiting similarity, although depth segregation could manifest itself through heightened habitat filtering as well. Furthermore, a comparison between estimates obtained using only diet‐associated traits, using only traits associated with coloration and visual adaptation, or the combination of both these types of traits might partition the causes of diversity in causes directly related to diet, and causes more related to sexual selection, an ongoing debate in the literature (Doorn, Noest, & Hogeweg, 1998; Kocher, 2004; Maan & Seehausen, 2011; Oneal & Knowles, 2013; Seehausen et al., 2014; Sobel, Chen, Watt, & Schemske, 2010). …”

Innovation: an emerging focus from cells to societies

“…This harkens to the idea that speciation generally entails both reproductive isolation and changes to the ecological niche (e.g. [130]); opening up a new niche (a key innovation) could facilitate the total number of new species, but does not necessarily increase the rates at which the species are formed. Rabosky argues that most tests of the predictions of key innovation have serious limitations, a central one being the low information content of many time-calibrated phylogenetic trees.…”