Session 52: Ichthyology Morphology & HistologyRoom: Ballroom 111C2022-07-31 15:30 - 16:30 |
| Moderator: Allison Bronson |
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1. 15:30 Investigating the features that facilitate sexual parasitism in male Anglerfishes (Teleostei, Ceratioidei). Sam Ghods*, University of Washington; Karly Cohen, University of Washington, Friday Harbor Laboratories; Luke Tornabene, University of Washington sghods2@uw.edu
Deep-sea anglerfishes (Ceratioidei) remain some of the most enigmatic fishes in the world. The sexual dimorphism seen in this group is the most extreme example amongst vertebrates. Male anglerfishes develop a specialized jaw called the denticular apparatus that is used to attach to females for reproduction. There are many questions regarding the biological mechanisms that facilitate this type of reproduction. The goals of the present study are to (1) describe the origin and structure of the denticular apparatus in male ceratioids with emphasis on the family Melanocetidae; (2) examine the ontogeny of male melanocetids to better define the metamorphic patterns; and (3) document similarities or differences in the denticular teeth and dermal spinules between taxa. Our results illustrate how dermal spinules and tooth-like structures of the denticular apparatus should be classified as odontodes, which represents a sixth radiation of odontodes in teleost fishes. Here we show that ceratioid anglerfishes develop odontodes that function as both body spines and as a secondary sexual trait, and we confirm that the denticular apparatus is a unique part of the cephalic skeleton not seen anywhere else in teleosts. Furthermore, we document male ontogeny within the family Melanocetidae to better understand the formative patterns of the denticular apparatus. The arrangement of male and female anatomies represents two different examples of the extreme phylogenetic economy of morphological parts, with females evolving lures from existing fin rays and males evolving secondary jaws from existing body spinules – both as apparent adaptions to life in the bathypelagic zone. |
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2. 15:45 How many modules does it take to build a brain? Using maximum likelihood to examine integration of the gymnotiform brain. Shannon Kuznar*, University of Louisiana at Lafayette; James Albert, University of Louisiana at Lafayette skuznar.shannon.kuznar@gmail.com
Modularity and the degree of integration among hypothesized phenotypic modules has recently been shown to affect rates and directions in the evolution of skull morphology of several vertebrate clades, where the module can be described as a unit within which there is high covariance, while integration describes the degree of covariance between modules. Although the skull and brain are developmentally coupled, studies on the degree of integration among brain modules are a still in their infancy. Here we examine patterns of brain evolution using a 3-D fiducial and semi-landmark-based scheme. We use contrast-stained computer tomography (CT) scans in 99 brains representing 23 gymnotiform species and 17 genera, comparing brain regions defined by functional, structural, and developmental criteria. Previous models have proposed differing numbers of modules within the gymnotiform brain, from three to seven or more. We use an EMMLi analysis to test alternative hypotheses in the literature of teleost brain evolution. We expect to find greater integration of brain regions in dolichocephalic than brachycephalic taxa, paralleling patterns observed in the braincase region of the neurocranium. We expect to find similar patterns of higher integration in the morphology of the gymnotiform brain of those taxa associated with generalized habitat and trophic utilization, and less integration (i.e. sub-functional partitioning) of brain regions associated with habitat and trophic specialization. |
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3. 16:00 Catch a Fish, Catch a Ride: How Alternate Methods of Piscivory Drive Divergent Patterns of Skull Evolution. JoJo West*, Rice University; Kory Evans, Rice University jjw8@rice.edu
Characterizing the relationship between form and function has been a longstanding goal of evolutionary biology. Convergence in lineages with distant phylogenetic relationships resulting from similar ecological niches has bolstered our understanding of the processes which drive morphological diversification. Still, the ambiguity in how exactly diversity arises when factoring in convergent evolution remains largely unsolved. Predation, a function which virtually all animals must perform, offers a direct look into understanding the relationship between form and function. Within piscivorous acanthomorph fishes, there are generally two strategies; lie-and-wait predation and pursuit predation. Here we use three-dimensional geometric morphometrics and a phylogenetic comparative toolkit to quantify the relationship between skull shape and prey capture mode across several disparate clades of piscivorous teleost fishes. We find that pelagic pursuit predators are more morphologically constrained than their counterparts, suggesting that ambush predation may facilitate diversification. |
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4. 16:15 Analysis of Craniofacial Evolution in Lake Victoria Cichlids based on CT-scans. Kassandra Ford*, University of Bern; Mikki Law, University of Bern; Pooja Singh, University of Bern; Kory Evans, Rice University; Ole Seehausen, University of Bern kassy159@gmail.com
The phenomenon of convergent evolution is often examined when similar morphologies appear within and across biological clades. African cichlids have many examples of convergence and parallel evolution in rapidly evolved phenotypes. However, most of the better-documented cases illustrate convergence between lakes and radiations. Here we study convergence within the Lake Victoria radiation that emerged over the last 15,000 years. Previous work primarily focused on oral and pharyngeal jaw morphology, but there has yet to be a comprehensive study on Lake Victoria species using the whole skull. This study examined 131 species (n=301) using CT-scanning and geometric morphometrics. We estimated a phylogenetic tree using whole-genome sequencing, assessed levels of convergence with R, and compared these data to dietary guilds. Our results show certain specialized phenotypes evolved multiple times within this clade, with significant levels of convergence. We also found that craniofacial morphology is closely tied to diet, particularly in species with specialized diets (i.e., algae scraping, mollusk crushing, and piscivory). Shape changes across this lineage fall into two major patterns: heterocephaly (relative braincase and snout size) and the proportion of head depth and head width. Both trends appear closely linked with diet, with discernable patterns correlating diet to head shape. Piscivores tend to have longer snouts with shallower heads, while crushers and scrapers have shorter snouts with deeper heads and larger, more robust supraoccipital bones. Additional examination is imperative to understanding how such a large diversity of craniofacial morphologies evolved in such a short period of time. |