Date of Award


Document Type


Degree Name

Master of Science (MS)


Biological Sciences

Committee Chair/Advisor

J. Antonio Baeza

Committee Member

Michael J. Childress

Committee Member

Vincent P. Richards


Contemporary and historical changes in marine environmental conditions influence biodiversity drastically. In marine invertebrates with highly dispersive planktonic larvae, diversification is facilitated or constrained by tectonic plate movements altering geography, prevailing current patterns, and climate. The decapod crustacean infraorder Achelata, which contains the spiny (fam. Palinuridae) and slipper (fam. Scyllaridae) lobsters, is characterized by a long-lived phyllosoma larvae stage. Panulirus is the most economically significant and speciose genus of spiny lobsters, with 20 recognized extant species and 5 subspecies distributed throughout shallow tropical and subtropical oceans worldwide. Diversification within these lineages has been proposed to be primarily driven by geological changes causing dispersal and vicariance events that affect population distribution and influence the settlement and dispersal potential of long-lived larvae by oceanic currents. To reveal phylogenetic relationships within the Achelata, maximum likelihood (ML) and Bayesian inference (BI) morphological and molecular phylogenies were constructed. Next, a historical biogeographic scenario for the Achelata was modeled on the time-calibrated molecular ML phylogeny. The Achelata and the Palinuridae emerged in the Tethys during the Triassic epoch. After the ancestor of Panulirus diverged during the late Jurassic (~161 Mya), Panulirus Lineages 1 and 2 originated in the Western and Indo-Pacific during the early (~133 Mya) and late (~85 Mya) Cretaceous. The genus Panulirus experienced the most diversification during the Eocene (~52 Mya), then continued to diversify until the Pliocene (~3 Mya), with the greatest concentration of Panulirus ancestral species existing in the Indo-West Pacific. Ultimately, Panulirus diversification occurred due to global dispersal and vicariance events from the late Jurassic to the Pliocene.

As Panulirus species and populations diverged in response to geographic change over time, they colonized habitats with variable environmental conditions and different selective pressures. Regional environmental conditions are known to drive the evolution of morphological, behavioral, and physiological traits in marine crustaceans. Therefore, the Achelata were also expected to respond to selective pressures on a molecular scale. As such, environmental conditions are expected to prompt the adaptive evolution of mitochondrial protein-coding genes (PCGs), which are vital for energy production via the oxidative phosphorylation pathway. I examined the effect of temperature and low oxygen on the adaptive evolution of mitochondrial PCGs. In the Achelata, mitochondrial PCGs exhibited a strong negative selection background. Signatures of positive selective pressure were detected in mitochondrial PCGs in equatorial Panulirus spp. inhabiting tropical equatorial regions with relatively consistent high temperatures and in deepwater Scyllaridae inhabiting low-oxygen depths. These results suggest that, following the initial diversification of Panulirus spp. temperature and oxygen levels have influenced the evolution of the 13 mitochondrial PCGs in equatorial Panulirus spp. and deepwater Scyllaridae. In general, this study has demonstrated how environmental conditions drive diversification as well as the adaptive evolution of mitochondrial PCGs in the Achelata.

Author ORCID Identifier




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