Morphology

The goal of these studies was to quantify mechanical properties of elasmobranch (sharks and batoids) skin to understand the functional relationships between mechanics and morphology, and how these correspond to differences in swimming and ecology. I relate mechanical behaviors with morphological structures to elucidate the underlying contributions of the skin toward elasmobranch skin mechanics. I mechanically tested skin in uniaxial tension to failure to assess the tensile strain at maximum load (extensibility), ultimate tensile strength, Young’s Modulus of elasticity (stiffness), and toughness among diverse groups of elasmobranchs. Across three chapters, I compare mechanical behaviors of the skin among species of sharks and batoids (separately) among body regions, and between sexes and axes of stress (longitudinal and hoop). Among 20 shark species, I quantified mechanical properties among ecomorphotypes and ontogenetically (across three maturity stages) and found that mechanical behaviors increase ontogenetically and are governed by two different underlying trends (maturity and ecomorphology). I found that shark skin oriented in the hoop direction was stronger and stiffer compared to skin oriented longitudinally, as hoop-oriented skin maintains internal volume and hydrostatic pressure by resisting deformation. Shark skin oriented longitudinally was more extensible, allowing for increased stretchability anteroposterior as a shark’s body undulates along the longitudinal axis. Dermal denticles (placoid scales), tooth-like structures of enameloid and dentine, are rooted in the stratum compactum layer of the dermis, embedded in a collagen fiber network.

Cryptic species remain poorly studied in octopuses. Following the reinstatement of the cryptic species, Octopus americanus, suggestions that it should supplant two taxa, Octopus vulgaris types I & II, in the western central and southwestern Atlantic Ocean, respectively, had yet been investigated in southeast Florida. To delineate this species, an integrative approach including morphological assessments and phylogenetic analyses of mitochondrial (16S & COI) and nuclear (rhodopsin) genes was employed. The utility of swabbing as a minimally invasive alternative DNA sampling method to tissue was also investigated. This taxon displays similar morphological traits to O. americanus. Maximum Likelihood phylogenetic inference placed this taxon in a highly supported monophyletic group with O. americanus. Both sampling methods delineated this taxon, though tissue was more successful. These results indicate that southeast Florida’s O. vulgaris-like species represents O. americanus. Thorough species delineation approaches advance our understanding of biodiversity, evolution, and ecology, and inform management practices.

Animals face both natural and sexual selection pressures, and at times, these pressures conflict with one another. This results in a tradeoff between sexual and natural selection. In my thesis, I examine aspects of Bachman’s sparrows’ behavior and morphology in relation to weather conditions in light of these two conflicting pressures.
Large bill size is selected for by the natural selection pressures of thermoregulation. Smaller bills are selected for by the sexual selection pressures of song quality. Both thermoregulation and song are important behaviors/processes that have fitness implications. By looking at bill size in relation to thermoregulatory ability and song quality I examined the tradeoff between these two selection pressures acting on the bill of Bachman’s sparrows

The functional impacts of olfactory rosette variation in elasmobranchs is unresolved. Our goal was to quantify rosette morphology and shape from 14 species using dissections, phylogenetic comparisons, and microCT imaging. We hypothesized that lamellar count and rosette shape (fineness ratio) would not scale with animal size, but internal rosette size variables must scale positively. We found that fineness ratio and lamellar counts varied significantly among species, and were positively correlated. The first two principal components of the pPCA explained 82% of the variation, with fineness ratio and lamellar count contributing the most. There were no significant differences between rosette structure or volume when comparing dissected values to in situ values obtained using diceCT. Based on our results, we hypothesize that variations in rosette shape and morphology will impact hydrodynamics and optimize odorant detection, and these data can be used to create 3D models for future hydrodynamic studies.

Estimating the sex of unknown human skeletal remains is important to the fields
of forensic anthropology, bioarchaeology, and other specialties. I studied sexual
dimorphism on the first and second ribs to estimate sex from skeletal remains. I
employed two approaches. I used geometric morphometrics to analyze landmark and
semilandmark coordinate points to examine the overall shape of the ribs. I also examined
the sternal end of the ribs for size using the superior-inferior height (SIH) and anteriorposterior
breadth (APB) in a binary logistic regression (BLR) model. Differences in male
and female first and second ribs are undetectable when landmark coordinate points are
used to capture shape variability, but significant differences in the shape of the ribs,
however, are detected through the use of semilandmark coordinate points.
Using semilandmark points to estimate sex presented an accuracy rate of 80.7%
from the first rib, and 72.9% from the second rib. The use of the sternal end presents
consistent results in its ability to estimate sex with an accuracy rate of 84.2%. The BLR model reveals significant differences between males and females than the geometric
morphometric approach; it is more applicable for discerning sexual dimorphism of
unknown individuals. This study reveals that while geometric morphometrics provides a
powerful approach to assessing morphological differences, it is not always better than
simpler methods, in this case, simple measurements analyzed through BLR.