Extrinsic Drivers of Diversification
The evolution of form and function is influenced by extrinsic factors (e.g., functional constraints, ecological interactions, natural selection) and/or intrinsic properties (e.g., modularity and integration). Tight interactions between fishes and their environment drive diversification of form and function in many groups of fishes.
"Shared ecological traits influence shape of the skeleton in flatfishes (Pleuronectiformes)" Black and Berendzen (2020): The flatfishes (Pleuronectiformes) are a unique and extraordinarily diverse group with remarkable asymmetry induced by ocular migration and a benthic lifestyle. I have shown that the majority of the diversity within the group evolved recently, within the past 15–10 million years in the middle Miocene, and is correlated with several ecological traits, including water type, diet, and sediment type, indicating an environmental role in the diversification of flatfishes Shared ecological traits influence shape of the skeleton in flatfishes (Pleuronectiformes). |
Diversity of skeletal morphology in the flatfishes.
|
Intrinsic Drivers of Diversification
In addition to extrinsic factors, intrinsic properties, like modularity and integration, can influence form and function. Modularity and integration are closely related concepts investigating how different units within an organism correlate.
"Integration and modularity in the diversity of the suckermouth armored catfishes" Black and Armbruster (In press in Royal Society Open Science): The suckermouth armored catfishes have a morphology that lends nicely to evolutionary modularity studies. Functional constraints, such as the fusion of the neurocranium and pectoral girdle, limit movement of the body's anterior part. In contrast, functional decouplings allow the oral jaws to move freely from other parts of the body. I discovered that the armored catfish body is highly modularized but has varying degrees of integration between the modules, suggesting modularity and integration are not all-or-nothing concepts. Additionally, the armored catfish subfamilies show differing patterns of evolutionary modularity and integration, suggesting that these various patterns have driven the subfamilies away from the ancestral shape, allowing for diversification along different trajectories. Royal Society Open Science |
Differences in modules between subfamilies within the armored catfishes.
|
Ecological interactions influence form and function
Ecology and morphology are correlated in animals, from insects to birds. Specifically, ecological interactions, like capturing and consuming prey, are essential drivers of evolution, specifically within the teleost fishes. Suction-feeding fishes have jaw shapes that are closely associated with diet type. Yet, these correlations have not been tested in fishes with more complex jaw functions. For example, armored catfishes have ventrally facing oral jaws, which are adhered to a surface to conduct feeding. Other studies have attempted to find a similar correlation between diet and oral jaw shape, but comparing such drastically different forms was impossible.
"Chew on this: Oral jaw shape is not correlated with diet type in Loricariid catfishes" Black and Armbruster (2022): To avoid the issues mentioned above, I used innovative landmarking techniques and cutting-edge phylogenetic comparative methods to capture the shape of the oral jaws and test the influence of ecology on form and function. Contrary to expectations, I found that the shape of the oral jaw does not correlate with diet, which suggests that form is not constrained to diet type. I also found that the evolutionary rates of jaw shape were associated with diet type, suggesting that as armored catfishes occupy various ecological niches, the oral jaws undergo faster shape changes, becoming more disparate. |
Oral jaw shape diversity in loricariid catfishes.
|
Stable Isotope Methods
"New method of isotopic analysis: Baseline Standardized Isotope Vector Analysis show trophic partitioning in loricariids." Black and Armbruster (2021):
"Stable isotope analyses have refined the study of trophic niche diversity within an ecosystem, yet traditional trophic partitioning methods may not be appropriate to identify variation among groups with similar dietary requirements. By building on vector-based analyses, we introduce a baseline-standardized isotopic vector analysis (BaSIVA) to visualize dietary variation while accounting for isotopic discrepancies between locations." Abstract from Black and Armbruster, 2021 |
Details for each species using BaSIVA.
|