Ecological diversification associated with the benthic‐to‐pelagic transition by North American minnows

Abstract

Ecological opportunity is often regarded as a key factor that explains why diversity is unevenly distributed across life. Colonization of novel environments or adaptive zones may promote diversification. North American minnows exhibit an ancestral benthic-to-pelagic habitat shift that coincided with a burst in diversification. Here, we evaluate the phenotypic and ecological implications of this habitat shift by assessing craniofacial and dietary traits among 34 species and testing for morphology-diet covariation, convergence and adaptive optima. There were several instances of morphology-diet covariation such as correlations between mouth angle and the consumption of terrestrial insects and between relative gut length and the consumption of algae. After accounting for size and phylogenetic nonindependence, benthic species had longer heads, longer snouts, eyes positioned higher on their head, smaller mouth angles and longer digestive tracts than pelagic minnows. Benthic minnows also consumed more algae but less terrestrial insects, by volume, than pelagic minnows. Lastly, there were three distinct evolutionary regimes and more convergence in morphology and dietary characteristics than expected under a Brownian motion model of evolution. These findings indicate that colonization of the pelagic zone by minnows involved myriad phenotypic and dietary changes associated with exploitation of terrestrial subsidies. Thus, minnows exhibit phenotype-dietary covariation, an expansion of ecological roles and a burst in diversification rates in response to the ecological opportunity afforded by the colonization of a novel habitat.

Is resource partitioning the key? The role of intra‐interspecific variation in coexistence among five small endemic fish species (Characidae) in subtropical rivers

“…Consumption of allochthonous resources, especially seeds, is common to many species of the neotropical region and does not appear to be accidental (Correa & Winemiller, 2014). In addition, in Other aquatic insects FISH studies with minnows in North America, cyprinid fishes with benthicpelagic habitats similar to those studied here, seeds were consumed from the water surface and water column, reinforcing the idea that the consumption of this type of resource seems to be a common pattern of species in this type of habitat (Burress et al, 2016). Although plant-based resources may have higher digestion costs, they can be advantageous in terms of low energy capture cost, i.e.…”

Ancient and contingent body shape diversification in a hyperdiverse continental fish radiation

“…; Burress et al. ), including multiple adaptive radiations (Schluter ; Schluter and Nagel ; Hollingsworth et al. ).…”

“…Habitat shifts may therefore be the missing drivers of body shape diversification in Characiformes. The results of the SURFACE analysis indicate at least three regime shifts (in Crenuchidae, Gasteropelecidae, and Serrasalmidae) in lineages transitioning across the benthic-pelagic habitat axis, which is a common diversification gradient in other freshwater fishes (Carlson and Wainwright 2010;Hollingsworth et al 2013;Burress et al 2016), including multiple adaptive radiations (Schluter 1995;Schluter and Nagel 1995;Hollingsworth et al 2013). Future analysis of body shape adaptation across macrohabitats in characiform subclades with well-established habitat transitions and uniform trophic ecology, like Crenuchidae, will offer insights into how habitat transitions may have influenced aspects of body shape evolution.…”

Adaptive radiation in labrid fishes: A central role for functional innovations during 65 My of relentless diversification

“…; Arbour and López‐Fernández ; Burress et al. ; Schenk and Steppan 2018). There are clearly a wide array of circumstances in which adaptive radiations occur and the early burst model does not fit all.…”

“…Since the end-Cretaceous mass extinction, coral reefs appear to have supported a diverse fish community ) that may have constrained early labrid diversification and prevented an abrupt response to ecological opportunity. In this sense, "continental radiations" that have largely diversified in the presence of antagonists may provide a better analogy for labrids; however, in four such radiations in which tests for early bursts of lineage and/or morphological evolution have been performed (Neotropical cichlids, South American rodents, and North American warblers and minnows), these clades have largely corroborated early burst patterns of diversification (Rabosky and Lovette 2008;López-Fernández et al 2013;Arbour and López-Fernández 2016;Burress et al 2016;Schenk and Steppan 2018). There are clearly a wide array of circumstances in which adaptive radiations occur and the early burst model does not fit all.…”