Abstract
Inter and intra-population variation in morphological traits, such as body size and shape, provides important insights into the ecological importance of individual natural populations. The radiation of Diaptomid species (~400 species) has apparently produced little morphological differentiation other than those in secondary sexual characteristics, suggesting sexual, rather than ecological, selection has driven speciation. This evolutionary history suggests that species, and conspecific populations, would be ecologically redundant but recent work found contrasting ecosystem effects among both species and populations. This study provides the first quantification of shape variation among species, populations, and/or sexes (beyond taxonomic illustrations and body size measurements) to gain insight into the ecological differentiation of Diaptomids. Here we quantify the shape of five Diaptomid species (family Diaptomidae) from four populations each, using morphometric landmarks on the prosome, urosome, and antennae. We partition morphological variation among species, populations, and sexes, and test for phenotype-by-environment correlations to reveal possible functional consequences of shape variation. We found that intraspecific variation was 18-35% as large as interspecific variation across all measured traits. Interspecific variation in body size and relative antennae length, the two traits showing significant sexual dimorphism, were correlated with lake size and geographic location suggesting some niche differentiation between species. Observed relationships between intraspecific morphological variation and the environment suggest that divergent selection in contrasting lakes might contribute to shape differences among local populations, but confirming this requires further analyses. Our results show that although Diaptomid species differ in their reproductive traits, they also differ in other morphological traits that might indicate ecological differences among species and populations.
Highlights
There is growing recognition that both interspecific and intraspecific variation can have significant effects on population, community, and ecosystem dynamics [1,2,3]
Freshwater fish with contrasting foraging phenotypes within [5] and among [6] populations can drive changes in community composition of prey and ecosystem processes [7,8]. These studies illustrate that intra-specific variation and local adaptation can influence ecosystem dynamics, and reveal that more work is needed to identify the specific phenotypes that underlie these population, community, and ecosystem effects [9]
Antennae length was approximately equal to body length (0.99% ± 0.05) for all species except the largest, Acanthodiaptomus denticornis, for which it was relatively short (0.87% ± 0.04)
Summary
There is growing recognition that both interspecific and intraspecific variation can have significant effects on population, community, and ecosystem dynamics [1,2,3]. Freshwater fish with contrasting foraging phenotypes within [5] and among [6] populations can drive changes in community composition of prey and ecosystem processes [7,8]. These studies illustrate that intra-specific variation and local adaptation can influence ecosystem dynamics, and reveal that more work is needed to identify the specific phenotypes that underlie these population, community, and ecosystem effects [9]. The shape of finch beaks on the Galapagos varies with resource use [16], the color and life-history of Trinidadian guppies varies with predation regimes [1], and the coat color of mouse populations varies with substrate type [17]
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