Cranial modularity drives phenotypic diversification and adaptive radiation of Antarctic icefishes

Proceedings of the National Academy of Sciences · 2025-09-29 · 2 citations

Modularity among traits is thought to drive morphological evolution and diversification, with more modular species often showing greater morphological disparity and faster evolutionary rates. However, recent studies suggest this pattern is not universal, as higher integration can sometimes be linked to faster rates of evolution. In adaptive radiation, modularity likely facilitates morphological divergence, but its specific role in trait diversification within these events remains uncertain. Antarctic icefishes (Perciformes: Notothenioidei) have undergone adaptive radiation in the frigid Southern Ocean, yet the role of modularity in their craniofacial evolution remains poorly understood. Emerging from a common ancestor 22 Mya, these fishes developed unique morpho-physiological adaptations, such as antifreeze glycoproteins, that contributed to their evolutionary success, but the contribution of cranial modularity to their diversification is still unexplored. Here, we analyze skull shape across 172 perciform species using micro-CT scanning and geometric morphometrics to investigate the tempo and mode of skull evolution in 80 notothenioids versus 92 perciform relatives. Notothenioids exhibit considerable cranial shape diversity, with skull shapes ranging from short to long faces. Fast rates of skull shape evolution occurred in smaller subclades following the emergence of cranial elongation, a derived trait within notothenioids. They also exhibit elevated evolutionary modularity relative to their perciform relatives, with reduced covariation among skeletal elements over time, likely corresponding with Miocene cooling events and the formation of the Antarctic Circumpolar Current. We propose that greater phenotypic modularity in notothenioid skulls represents a pivotal innovation, facilitating their evolutionary response to new ecological opportunities in the Antarctic.

Geologic History Explains Freshwater Fish Species Richness Across the Conterminous <scp>USA</scp>

Global Ecology and Biogeography · 2025-10-01 · 1 citations

Aim: Freshwater fishes comprise over 20% of vertebrate biodiversity despite occupying <1% of the Earth's surface. However, species richness differs substantially among river basins. Fundamentally, richness patterns can be explained by spatial variation in diversification rates, evolutionary time, and habitat capacities, which are in turn shaped by landscape change over geologic timescales. To test how geologic disturbances have influenced the accumulation of freshwater fish biodiversity, we hypothesized species richness would be (1) ordered by regional geologic history, (2) associated with high or intermediate river capture rates, (3) higher in assemblages with older evolutionary origins, and (4) positively associated with stream size. Time Period: 2008-2019. Location: Conterminous United States (USA). Major Taxa: Freshwater fishes. Methods: We analyzed native species richness from a spatially representative survey of 5,321 fish assemblages at 3,609 sites. Geologic history was determined from surrogates of tectonic activity, glaciation, sea levels, and river capture over the last 66 million years, which were paired with previously published evolutionary time estimates. Hypotheses were tested with spatial linear models. Results: All hypotheses were at least partially supported. (1) Rank-order richness matched hypothesized effects of geologic disturbances on evolutionary time and diversification rates. (2) Richness peaked in lowlands with high putative river capture rates. (3) Richness increased with evolutionary time at broad scales, but this relationship was weak and influenced by non-teleost taxa. (4) Richness largely increased with stream size.Overall, the tectonically active western USA exhibited lower richness, weaker effects of stream size, and a greater share of young lineages compared to the more geologically stable eastern USA, especially unglaciated lowlands within the Mississippi Basin. Main Conclusions: We demonstrate that deep-time processes leave a persistent mark on fish species richness. Thus, accounting for geologic history can improve assessments of freshwater biodiversity and biological condition in the USA and beyond.

Distinct evolutionary signatures underlie body shape diversity across deep sea habitats

Evolution · 2025-10-10

The deep sea is known for challenging abiotic and biotic conditions; yet, deep-sea fishes have been shown to have higher phenotypic diversity than shallow relatives. An open question is whether different habitats within the deep sea differentially contribute to this surprising phenotypic diversity. Here, we explore the joint effects of two major environmental dimensions, the benthic-pelagic axis and ocean depth, on body shape diversification in marine teleost fishes. We found that increasing ocean depth shifted axes of phenotypic evolution and promoted diversification for benthic, demersal, and pelagic fishes alike. However, body shape diversity and rates of body shape evolution did not scale consistently across habitats. For benthic fishes, rate increased more strongly than diversity with increasing ocean depth, while the reverse was true for pelagic fishes. Analyses of habitat transitions suggested that independent invasions may help explain the diversity of deep-pelagic fishes without invoking high evolutionary rates. Relaxed selection may also explain this diversity, as suggested by the wide range of deep-pelagic forms observed along an evolutionary axis of body elongation. Overall, our results reveal a mosaic of pathways through which body plan diversity accumulated across a vertebrate radiation, underscoring the importance of considering finer-scale habitat variation in broad-scale studies.

Colonization Dynamics Explain the Decoupling of Species Richness and Morphological Disparity in Syngnatharian Fishes across Oceans

The American Naturalist · 2024-11-12 · 1 citations

AbstractA clear longitudinal gradient in species richness across oceans is observed in extant marine fishes, with the Indo-Pacific exhibiting the greatest diversity. Three non-mutually-exclusive evolutionary hypotheses have been proposed to explain this diversity gradient: time for speciation, center of accumulation, and in situ diversification rates. Using the morphologically disparate syngnatharians (seahorses, dragonets, goatfishes, and relatives) as a study system, we tested these hypotheses and additionally assessed whether patterns of morphological diversity are congruent with species richness patterns. We used well-sampled phylogenies and a suite of phylogenetic comparative methods (including a novel phylogenetically corrected Kruskal-Wallis test) that account for various sources of uncertainty to estimate rates of lineage diversification and morphological disparity within all three major oceanic realms (Indo-Pacific, Atlantic, and eastern Pacific), as well as within the Indo-Pacific region. We find similar lineage diversification rates across regions, indicating that increased syngnatharian diversity in the Indo-Pacific is due to earlier colonizations from the Tethys Sea followed by in situ speciation and more frequent colonizations during the Miocene coinciding with the formation of coral reefs. These results support both time for speciation and center of accumulation hypotheses. Unlike species richness unevenness, shape disparity and evolutionary rates are similar across oceans because of the early origin of major body plans and their subsequent spread via colonization rather than in situ evolution. Our results illustrate how species richness patterns became decoupled from morphological disparity patterns during the formation of a major biodiversity hot spot.

Reduced evolutionary constraint accompanies ongoing radiation in deep-sea anglerfishes

Nature Ecology & Evolution · 2024-11-27 · 14 citations

Many ways to build an angler: diversity of feeding morphologies in a deep-sea evolutionary radiation

Biology Letters · 2023-06-01 · 16 citations

Almost nothing is known about the diets of bathypelagic fishes, but functional morphology can provide useful tools to infer ecology. Here we quantify variation in jaw and tooth morphologies across anglerfishes (Lophiiformes), a clade spanning shallow and deep-sea habitats. Deep-sea ceratioid anglerfishes are considered dietary generalists due to the necessity of opportunistic feeding in the food-limited bathypelagic zone. We found unexpected diversity in the trophic morphologies of ceratioid anglerfishes. Ceratioid jaws span a functional continuum ranging from species with numerous stout teeth, a relatively slow but forceful bite, and high jaw protrusibility at one end (characteristics shared with benthic anglerfishes) to species with long fang-like teeth, a fast but weak bite and low jaw protrusibility at the other end (including a unique 'wolftrap' phenotype). Our finding of high morphological diversity seems to be at odds with ecological generality, reminiscent of Liem's paradox (morphological specialization allowing organisms to have broader niches). Another possible explanation is that diverse ceratioid functional morphologies may yield similar trophic success (many-to-one mapping of morphology to diet), allowing diversity to arise through neutral evolutionary processes. Our results highlight that there are many ways to be a successful predator in the deep sea.

Author response for "Many ways to build an angler: diversity of feeding morphologies in a deep-sea evolutionary radiation"

2023-05-29

Historical biogeography supports Point Conception as the site of turnover between temperate East Pacific ichthyofaunas

PLoS ONE · 2023-09-19 · 10 citations

The cold temperate and subtropical marine faunas of the Northeastern Pacific meet within California as part of one of the few eastern boundary upwelling ecosystems in the world. Traditionally, it is believed that Point Conception is the precise site of turnover between these two faunas due to sharp changes in oceanographic conditions. However, evidence from intraspecific phylogeography and species range terminals do not support this view, finding stronger biogeographic breaks elsewhere along the coast. Here I develop a new application of historical biogeographic approaches to uncover sites of transition between faunas without needing an a priori hypothesis of where these occur. I used this approach to determine whether the point of transition between northern and southern temperate faunas occurs at Point Conception or elsewhere within California. I also examined expert-vetted latitudinal range data of California fish species from the 1970s and the 2020s to assess how biogeography could change with the backdrop of climate change. The site of turnover was found to occur near Point Conception, in concordance with the traditional view. I suggest that recent species- and population-level processes could be expected to give signals of different events from historical biogeography, possibly explaining the discrepancy across studies. Species richness of California has increased since the 1970s, mostly due to species's ranges expanding northward from Baja California (Mexico). Range shifts under warming conditions seem to be increasing the disparity between northern and southern faunas of California, creating a more divergent biogeography.

Historical biogeography supports Point Conception as the site of turnover between temperate East Pacific ichthyofaunas

bioRxiv (Cold Spring Harbor Laboratory) · 2023-05-13

ABSTRACT The northern and southern marine faunas of the temperate Northeastern Pacific meet within California as part of one of the few eastern boundary upwelling ecosystems of the world. Traditionally, it is believed that Point Conception is the precise site of turnover between these two faunas due to sharp changes in oceanographic conditions. However, evidence from intraspecific phylogeography and species range terminals do not support this view, finding stronger biogeographic breaks elsewhere along the coast. Here I develop a new application of historical biogeographic approaches to uncover sites of transition between faunas without needing an a priori hypothesis of where these occur. I used this approach to determine whether the point of transition between northern and southern temperate faunas occurs at Point Conception or elsewhere within California. I also take advantage of expert-vetted latitudinal range data of California fish species from the 1970s and the 2020s to assess how biogeography could change with the backdrop of climate change. The site of turnover was found to occur near Point Conception, in concordance with the traditional view. I suggest that recent species- and population-level processes such as dispersal and speciation could be expected to give signals of different events from historical biogeography, possibly explaining the discrepancy across studies. Species richness of California has increased since the 1970s, mostly due to new species from Baja California. Range shifts under warming conditions will have the consequence of increasing the disparity between northern and southern faunas of California, creating a more divergent biogeography.

Author response for "Many ways to build an angler: diversity of feeding morphologies in a deep-sea evolutionary radiation"

2023-04-14