Size variation facilitates population divergence but does not explain it all: an example study from a widespread African monkey

Abstract

Subspecific variation is widespread in vertebrates. Within Africa, several mammals have extensive geographic distributions with attendant morphological, ecological, and behavioural variations, which are often used to demarcate subspecies. In the present study, we use a primate species, the vervet monkey, Cercopithecus aethiops, as a case study for intraspecific divergence in widespread mammals, assessed through hard tissue morphology. We examine intraspecific differences in size, shape, and non-allometric shape from a taxonomic perspective, and discuss the macroevolutionary implications of findings from microevolutionary analyses of geographic variation. A geometric morphometric approach was used, employing 86 three-dimensional landmarks of almost 300 provenanced crania. Many of the taxonomic differences in skull morphology between vervet populations appear to be related to geographic proximity, with subspecies at opposite extremes of a west-to-east axis showing greatest divergence, and populations from central and south Africa being somewhat intermediate. The classification rate from discriminant analyses was lower than that observed in other African primate radiations, including guenons as a whole and red colobus. Nonetheless, taxonomic differences in shape were significant and not simply related to either geography or size. Thus, although shifts in size may be an important first step in adaptation and diversification, with size responding more quickly than shape to environmental change, the six vervet taxa currently recognized (either as species or subspecies) are not simply allometrically scaled versions of one another and are probably best viewed as subspecies. Holding allometry constant when examining inter-population differences in shape may thus help to reveal the early stages of evolutionary divergence. The vervet case study presented here hence has relevance for future studies examining intraspecific differentiation in other large mammals, particularly through the methods used to identify small but biologically meaningful divergence, with attendant implications for conservation planning. (C) 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 101, 823-843

Exploring morphological generality in the Old World monkey postcranium using an ecomorphological framework

“…, ; Elton et al. ). Geographic variation in guenon postcrania has received relatively little attention, primarily because of the paucity of specimens available that sample a representative proportion of the total range.…”

Biogeographic variation in the baboon: dissecting the cline

“…Discriminant function analysis (DFA) was used to assess the degree of similarity of subspecies (Elton et al 2010). The ratio of misclassified and correctly classified individuals, after cross-validation, gives a measure of similarity (Cardini & Elton, 2011).…”

Localized population divergence of vervet monkeys (Chlorocebusspp.) in South Africa: Evidence from mtDNA

“…Although geography and spatially-structured environmental variables – such as rainfall and seasonality – explained some of this localized variation, 60–80% remained unexplained. Further study by this group found localized variation within vervets to be of particular interest because of evident plasticity of vervets leading to rapid expansion into previous underutilized areas that could lead to localized adaptive response to microclimates; the authors characterized such local variation as ‘incipient stages in a process of evolutionary radiation’ (Elton et al 2010). Large-scale genetic studies have also attempted to explain taxon-wide variation.…”

“…Despite work having been done in this region for quite some time (e.g., Henzi & Lucas, 1980), and the ongoing deep phenotyping being conducted within the area, very little is yet known about local population processes. Although recent extensive taxonomic sampling has been able to compare East African to South African extensions of the pygerythrus range (Haus et al, 2013, Elton et al, 2010) they did not sample sufficiently in South Africa to address local population divergences with any resolution. Such finer scale work has been done in the East African aethiops morph, or grivets, in which evidence was found of mtDNA substructuring despite widespread monotypy in phenotype, perhaps as the result of demographic shifts due to climatic change (Shimada, 2000; Shimada et al 2002).…”