Biology subjects

Winemiller, K. O.

Publications and source records attributed to Winemiller, K. O..

3 recordsLinked to original sources

bioRxiv2025

What determines trophic niche breadth? A global analysis of freshwater fishes using isospaces

Trophic niche is one of the most tractable dimensions of a species niche. Several hypotheses have been proposed to explain global variation in species trophic niches, but empirical tests are limited. Stable isotope analysis (SIA) of {delta}{superscript 1}3C (a proxy for basal sources) and {delta}{superscript 1} N (a proxy for vertical trophic position) has increasingly been used to estimate trophic niche variation. We performed SIA on a dataset of over 33,000 stable isotope samples from freshwater fishes across six ecoregions. For 541 populations (358 species), we estimated the size of {delta}{superscript 1}3C x {delta}{superscript 1} N isospace--a bivariate representation of trophic niche breadth. We evaluated isospace variation in relation to environmental factors, species traits, and sampling scale, testing both novel and long-standing hypotheses about the drivers of trophic niche variation. A Boosted Regression Tree Model best predicted isospace, with environmental and trait-based variables among the strongest predictors. Fish isospaces were broader in regions with warmer temperatures, higher humidity, and precipitation variability, suggesting that more productive, diverse, and seasonal ecosystems are associated with broader trophic niches. Conversely, isospace size declined with increasing basin fish richness, which may reflect heightened interspecific competition or historical competitive exclusion. Isospace size was slightly smaller in large lakes compared to rivers, streams, and small lakes. Within-population variation in body size was strongly and positively associated with isospace size, highlighting the role of ontogenetic dietary shifts. Fish with truncate-rounded fins had broader isospaces than those with forked-lunate fins, likely due to the former having more limited movement and greater spatial isolation that resulted in greater between-individual niche variation. Primary consumers had larger isospaces than intermediate and top consumers. Predators showed relationships consistent those observed from analysis encompassing all trophic guilds, but non-predators deviated with regards to four variables--solar radiation, basin richness, average body size, and caudal fin aspect ratio. Isospace size increased with the number of sampled individuals, habitats and years surveyed. Although isospace patterns have well-documented limitations as trophic ecology metrics, our findings nonetheless conform with several longstanding hypotheses for trophic niche variation and stimulate new ideas about environmental and biological drivers of niche breadth.

ecology↗

bioRxiv2021

Derived loss of signal complexity and plasticity in a genus of weakly electric fish

Signal plasticity can maximize the usefulness of costly animal signals such as the electric organ discharges (EODs) of weakly electric fishes. Some species of the order Gymnotiformes rapidly alter their EOD amplitude and duration in response to circadian cues and social stimuli. How this plasticity is maintained across related species with different degrees of signal complexity is poorly understood. In one genus of weakly electric gymnotiform fish (Brachyhypopomus) only one species, B. bennetti, produces a monophasic signal while all other species emit complex biphasic or multiphasic EOD waveforms produced by two overlapping but asynchronous action potentials in each electric organ cell (electrocyte). One consequence of this signal complexity is the suppression of low-frequency signal content that is detectable by electroreceptive predators. In complex EODs, reduction of the EOD amplitude and duration during daytime inactivity can decrease both predation risk and the metabolic cost of EOD generation. We compared EOD plasticity and its underlying physiology in Brachyhypopomus focusing on B. bennetti. We found that B. bennetti exhibits minimal EOD plasticity, but that its electrocytes retained vestigial mechanisms of biphasic signaling and vestigial mechanisms for modulating the EOD amplitude. These results suggest that this species represents a transitional phenotypic state within a clade where signal complexity and plasticity were initially gained and then lost. We discuss potential the roles of signal mimicry, species recognition, and sexual selection in maintaining the monophasic EOD phenotype in the face of detection by electroreceptive predators.

physiology↗

bioRxiv2018

Osmoregulation in freshwaters: Gene expression in the gills of a Neotropical cichlid in contrasting pH and ionic environments

Freshwater habitats of the Neotropics exhibit a gradient from relatively neutral, ion-rich whitewater to acidic, ion-poor blackwater. Closely related species often show complementary distributions among ionic habitats, suggesting that adaptation to divergent osmoregulatory environments may be an important driver of Neotropical fish diversity. However, little is known about the evolutionary tradeoffs involved in ionoregulation across distinct freshwater environments. Here, we surveyed gill mRNA expression of Cichla ocellaris var. monoculus, a Neotropical cichlid, to examine cellular and physiological responses to experimental conditions mimicking whitewater and blackwater.\n\nGene ontology enrichment of expressed genes indicated that the gills were remodeled during both forms of environmental challenge, with changes biased towards the cellular membrane. We observed expression of signaling pathways from both the acute and extended response phases, including evidence that growth hormone (GH) may mediate osmoregulation in whitewater through paracrine expression of insulin-like growth factor I (IGF-I), but not through the GH receptor, which instead showed correlated up-regulation with the prolactin receptor and insulin-like growth factor II in blackwater.\n\nDifferential expression of genes related to paracellular tight junctions and transcellular ion transport showed responses similar to euryhaline fishes in fresh versus seawater, with some exceptions, suggesting that relaxed ion retention via the gills, possibly mediated by the GH/IGF-I axis, is a strong candidate for evolutionary modification in whitewater and blackwater endemic populations. In each osmoregulatory domain, we saw examples of contrasting differential expression of paralogs of genes that are single copy in most terrestrial vertebrates, indicating that adaption by fishes to diverse physicochemcial environments has capitalized on diversification of osmoregulatory gene families.

ecology↗