Biology subjects

McGuire, J. A.

Publications and source records attributed to McGuire, J. A..

3 recordsLinked to original sources

bioRxiv2022

Oxygen availability drives blood traits and the cell number-size tradeoff across Andean hummingbirds

Predictable trait variation across environmental gradients suggests that adaptive evolution repeatedly finds the same solution to a challenge. Trait-environment associations can reflect long-term, genetic evolution across phylogenies, or short-term, plastic responses of individuals. When phylogenetic and population-level patterns match, it implies consistency between the long timescale of adaptation and the short timescale of acclimatization. Alternatively, genetic adaptation can find solutions that break the rules of trait-environment covariation. For example, blood-hemoglobin concentration ([Hb]) increases at high elevations in animals, but genetic adaptations in some populations have been shown to augment tissue oxygenation while curtailing hemoglobin production, altering this predictable [Hb]-elevation association. Here, we tested whether species adaptation to elevation generally alters trait-environment relationships for blood. To do this, we measured blood traits of 1,217 individuals representing 77 species of Andean hummingbirds, across a 4,600 m elevational gradient. We used hierarchical Bayesian modeling to estimate blood trait responses to elevation, environmental temperature, precipitation, individual and species characteristics, and phylogeny. Strikingly, the effects of elevation on [Hb] and hematocrit (Hct) were nearly identical for individuals and species, implying that rules of elevational blood variation are set by physics of gas exchange in the hummingbird respiratory system and are unchanged by species adaptation. However, when we looked at mechanisms of [Hb] adjustment--by changes in red blood cell size or number--we did find a signal of species adaptation: To adjust [Hb], species at low and high elevations, respectively, tended to adjust cell size, whereas species at mid-elevations tended to adjust cell number. Despite scale-independent elevational variation in [Hb] and Hct, the species-specific balance of red blood cell size versus number appears to have been affected by adaptations that distinguish hummingbird species living at moderate versus high elevations.

evolutionary biology↗

bioRxiv2019

Recent and rapid colonization of the Lesser Sundas Archipelago from adjacent Sundaland by seven amphibian and reptile species

The Lesser Sundas Archipelago is comprised of two parallel chains of islands that extend between the Asian continental shelf (Sundaland) and Australo-Papuan continental shelf (Sahul). These islands have served as stepping-stones for taxa dispersing between the Asian and Australo-Papuan biogeographic realms. While the oceanic barriers have prevented many species from colonizing the archipelago, a number of terrestrial vertebrate species have colonized the islands either by rafting/swimming or human introduction. Here we examine phylogeographic structure within the Lesser Sundas for three snake, two lizard, and two frog species that each have a Sunda Shelf origin. These species are suspected to have recently colonized the archipelago, though all have inhabited the Lesser Sundas for over 100 years. We sequenced mtDNA from 230 samples to test whether there is sufficiently deep genetic structure within any of these taxa to reject human-mediated introduction. Additionally, we tested for genetic signatures of population expansion consistent with recent introduction, and estimated the ages of Lesser Sundas clades, if any exist. Our results show little to no genetic structure between populations on different islands in five species, and moderate structure in two species. Nucleotide diversity is low for all species, and the ages of the most recent common ancestor for species with monophyletic Lesser Sundas lineages date to the Holocene or late Pleistocene. These results support the hypothesis that these species entered the archipelago relatively recently and either naturally colonized or were introduced by humans to most of the islands within the archipelago within a short time span.

zoology↗

bioRxiv2018

Sexual Dichromatism Drives Diversification Within a Major Radiation of African Amphibians

Theory predicts that sexually dimorphic traits under strong sexual selection, particularly those involved with intersexual signaling, can accelerate speciation and produce bursts of diversification. Sexual dichromatism (sexual dimorphism in color) is widely used as a proxy for sexual selection and is associated with rapid diversification in several animal groups, yet studies using phylogenetic comparative methods to explicitly test for an association between sexual dichromatism and diversification have produced conflicting results. Sexual dichromatism is rare in frogs, but it is both striking and prevalent in African reed frogs, a major component of the diverse frog radiation termed Afrobatrachia. In contrast to most other vertebrates, reed frogs display female-biased dichromatism in which females undergo color transformation, often resulting in more ornate coloration in females than in males. We produce a robust phylogeny of Afrobrachia to investigate the evolutionary origins of sexual dichromatism in this radiation and examine whether the presence of dichromatism is associated with increased rates of net diversification. We find that sexual dichromatism evolved once within hyperoliids and was followed by numerous independent reversals to monochromatism. We detect significant diversification rate heterogeneity in Afrobatrachia and find that sexually dichromatic lineages have double the average net diversification rate of monochromatic lineages. By conducting trait simulations on our empirical phylogeny, we demonstrate our inference of trait-dependent diversification is robust. Although sexual dichromatism in hyperoliid frogs is linked to their rapid diversification and supports macroevolutionary predictions of speciation by sexual selection, the function of dichromatism in reed frogs remains unclear. We propose that reed frogs are a compelling system for studying the roles of natural and sexual selection on the evolution of sexual dichromatism across both micro- and macroevolutionary timescales.

evolutionary biology↗