Marine organisms inhabit an environment where there are few absolute barriers to movement. In addition, a planktonic larval stage is common to most marine fishes and invertebrates. Consequently, marine organisms are often characterized by little genetic differentiation over large geographic distances, and the factors that might generally promote genetic divergence are not well understood. Here, contributions to population structure from both intrinsic and extrinsic factors were investigated in Gulf of California blennioid fishes. In Appendix A, population structure was estimated from mtDNA control region sequences for three species, Axoclinus nigricaudus, Malacoctenus hubbsi, and Ophioblennius steindachneri, that differ in predicted dispersal patterns (based on ichthyoplankton distribution and abundance patterns relative to rock reefs). FST ranged widely among low to high predicted dispersal species, in the same rank order predicted by larval distribution patterns. In A. nigricaudus (low predicted dispersal), phylogenetic, population genetic, and general linear model analyses of mtDNA (Appendix B) showed that variation was significantly partitioned between two biogeographic regions, and that geographic distance and unsuitable habitat also contributed to mtDNA differentiation. In contrast, allozyme variation in A. nigricaudus showed less partitioning than mtDNA and there was no break between biogeographic regions (Appendix C). In Gulf of California blennies, I find that population structure varies among fishes that have a planktonic larval stage in a manner that can be predicted from larval distribution patterns. The correlation between larval distribution and population structure suggests that some fish larvae, such as A. nigricaudus, actively maintain a position close to their natal reef, preventing substantial gene flow among many populations. In addition, patterns of population subdivision in A. nigricaudus (low dispersal) indicate that when dispersal is restricted, substantial population subdivision due to a combination of factors can occur, despite having a planktonic larval stage. The discordance between mtDNA and allozymes in A. nigricaudus is consistent with non-equilibrium conditions following a population perturbation, selection on allozymes or mtDNA, or some combination of these factors. These results emphasize that multiple genetic markers should be examined when making inferences about the genetic structures of natural populations.

I studied the East Pacific green turtle, Chelonia mydas agassizii , at the Bahia de los Angeles foraging grounds of the Gulf of California from July 1995 to October 1999. Entanglement nets were used to capture 153 green turtles among 16 capture sites. Pooled straight carapace length (SCL; mean ± SE) was 75.1 ± 0.79 cm. Though there was no significant variation in mean SCL among years, there was evidence of a difference in mean SCL among capture sites. Most of the population (58%) consisted of immature turtles but did not differ significantly from a 1:1 immature:adult ratio. Pooled adult sex ratio (F:M) was biased toward probable females (2.70:1.00) and differed substantially from a 1:1 ratio. Approximately 5% of the population showed signs of anthropogenic-derived injuries ranging from missing flippers to boat impact scars. I collected gastric lavage samples from 101 green turtles and fecal samples from a subset of 45 turtles. Digestive tract contents were analyzed from seven stranded carcasses. The primary alga recovered in diet samples was Gracilariopsis lemaneiformis. Other major diet items included the green algae Codium sp. and Ova lactuca. Animal matter was found in all sample types. Tube worms (Sabellidae), sponges (Porifera), sea hares (Aplysia vaccaria), and sea pens ( Ptilosarcus undulatus) were the most commonly ingested invertebrates. I studied home range sizes and movements of 23 C. m. agassizii . Mean minimum convex polygon home range area was 1,801 ha. Kernel density estimates (95%) of home range area had a mean of 1,545 ha. Home range length averaged 7,548 m. Mean 24-h vagility was 9,535 m. Diurnal and nocturnal movements were evident. Turtles exhibited a bimodal pattern in which they foraged in nearshore algae pastures during evening and night hours and moved to offshore and/or insular resting sites by midmorning. This study indicates that Bahia de los Angeles is an important foraging and developmental habitat for C. m. agassizii. Management efforts should focus on reducing human disturbance and the use of entanglement nets in the entire bay. In such efforts it is essential that local inhabitants are provided with alternatives that encourage sustainable marine resource use and economic progress.

Phenotypic plasticity has been proposed as an adaptive mechanism by which organisms can maximize their fitness in response to short-term environmental variability. In this dissertation, I test one prediction that comes out of this idea: that populations from more variable environments should have higher levels of phenotypic plasticity than populations from less variable environments. I first analyzed precipitation variability and predictability across nine biomes in the Southwestern U.S. to determine a gradient of environmental variability. There was a non-linear negative relationship between precipitation variability and precipitation mean. In general, contrary to common belief, desert biomes were no more variable nor less predictable than nondesert biomes. I tested the relationship between environmental variability and phenotypic plasticity in seven populations of the pallid-winged grasshopper (Trimerotropis pallidipennis). Contrary to prediction, populations from more variable environments had lower, not higher, levels of phenotypic plasticity in development time. There was a significant convex quadratic relationship between plasticity for size at maturity and precipitation variability. In general, females in populations with more plasticity in development time had lower fitness. Plasticity in size at maturity generally did not affect fecundity, but increased survivorship. Plasticities in both traits conferred no significant costs or benefits in males. I tested the hypothesis that these results were due to constraints on the evolution of plasticity: either to a lack of genetic variation for plasticity or to antagonistic pleiotropy between size at maturity and development time. I found sufficient genetic variation for plasticity to evolve in all study populations and little evidence for antagonistic pleiotropy. I further tested whether selection for developmental stability or directional selection for short development time could explain the pattern of plasticity responses across the gradient. Low plasticity responses were apparently due to selection for developmental stability in deserts. I found weak evidence that antagonistic and synergistic selection could also explain the plasticity responses. I found no evidence that directional selection for short development time in all environments could explain the lower levels of phenotypic plasticity in the desert populations.

The Tachinidae is a taxonomically and ecologically diverse clade of parasitoids for which evolutionary and ecological relationships with hosts are largely unknown. Here, I employed a multidisciplinary approach to evaluate the determinants of patterns of host use in the Tachinidae. First, I examined spatio-temporal variation in the tachinid-dominated parasitoid assemblage of one lepidopteran species Grammia geneura . The parasitoid assemblage and parasitism rates varied dramatically among and within sampling sites, seasons, and years. I show that this variability may be a function of habitat-specific parasitism and indirect interactions between this host and other Macrolepidoptera through shared tachinid parasitoids. I then experimentally examined the host selection process in the tachinid Exorista mella. Host movement was an important elicitor of attack behavior. Flies also responded to odors associated with food plants of their host. Experienced flies attacked hosts more readily than did inexperienced flies. Based on these results, I proposed a host selection scenario for this tachinid species. E. mella also teamed to associate colors with hosts and avoided deterrent models that they had experienced. However, I failed to find evidence for odor learning. Learning of host-associated cues by E. mella may allow this parasitoid to take advantage of abundant host populations and maintain host-searching efficiency in an unpredictable environment. To examine how host-associated characteristics evolved in the Tachinidae, I reconstructed the evolutionary relationships within the subfamily Exoristinae using molecular data. Phylogenetic analyses generally supported recent classifications. Analyses of host-related characters indicated that tachinids show great evolutionary lability in behavior, morphology, and host range. Finally, I sampled host species to assess the determinants of tachinid community structure and host range. Several host characteristics were found to affect tachinid species richness. These patterns may be due to the opportunistic use of abundant hosts by polyphagous tachinids, enemy-free space provided by well-defended hosts, and the process of host location. Patterns of tachinid host use varied significantly with sample size, host diet breadth, host gregariousness, plant form, and host morphology. Taken together, these studies indicate high levels of plasticity in tachinid-host associations. This may be responsible for their ecological and evolutionary success.

Frankliniella occidentalis response to color hue and intensity was tested in both field bioassays and electrophysiology of the thrips eye. Results of electroretinograms demonstrated that males and females have a double peak spectral efficiency in the ultraviolet near 365nm and in the green-yellow range at 540nm. Results of field tests suggest, based on density change relative to sex ratio change between behaviors, that there was a greater change in male behavior (i.e. density) than in female behavior. Higher densities of thrips were observed on blue, violet, white and yellow hues. Interactions between the UV and green photopigments and integration of visual stimuli within the central nervous system may allow for discrimination of blue and violet colors, that are at wavelengths between the two peaks. Because the peaks of spectral sensitivity and the relative efficiency are the same between sexes, and the relative rankings of density remains the same between behavior periods, the greater change in male versus female behavior may be the result of complex behavioral responses to many possible cues as yet undetermined.

Taxon sampling is explicitly examined using simulations and probability analyses. The simulations focus on the ability of two different sampling strategies to correctly reconstruct relationships among subgroups of taxa. One sampling strategy chooses taxa randomly, the other strategy chooses taxa to increase the phylogenetic dispersal of the taxa. Also considered is whether the inclusion of a single basal taxon will increase the frequency of correctly reconstructing the relationships among subgroups. Inclusion of the basal taxon is found to decrease success (correct subgroup relationships). The strategies are found to differ, primarily due to differing tendencies to include the basal taxon (the random strategy includes the basal taxon less frequently and outperforms the dispersed strategy). The inclusion of a basal taxon is also found to decrease the probability of correctly reconstructing ancestral character states. The probability of randomly choosing a single taxon from one side of the root is developed.

<p>White croaker (<i>Genyonemus lineatus</i> family: Sciaenidae) are a benthic foraging fish associated with soft sediment and wastewater outfalls in Southern California. While they are used as a sentinel species due to their high organochlorine contaminant loads, little is known of their movements in relation to contaminated habitats. Acoustic telemetry was used to characterize the site fidelity, area use, and dispersal of 97 white croaker on the Palos Verdes Shelf, California. White croaker demonstrated generally low, but highly variable residency and recurrence to the Palos Verdes Shelf and exhibit nomadic movement patterns. Although the entire monitored shelf was visited by white croaker, habitats in proximity to wastewater outfalls and between 25&ndash;35 m depth were preferentially used. Approximately half of white croaker migrated into Los Angeles Harbor. These data are vital for understanding organochlorine contaminant exposure for planning future remediation and monitoring. </p>

<p> Between August 2010 and September 2012, acoustic telemetry was used to monitor movements of 31 Yellow Snapper and 25 Leopard Grouper at Los Islotes reserve, a small rocky reef and reported spawning site for both species in the southwest Gulf of California. Overall, both species exhibited site fidelity to Los Islotes (grouper: present 64 f 30% of days; snapper: 49 &plusmn; 30%). Both species frequented rock and wall habitats; though snapper showed greater site attachment to specific portions of the reserve, grouper exhibited greater site fidelity to the entire reserve. Approximately 30% of snapper showed indications of spawning-related migrations elsewhere in the Gulf, though no clear seasonal pattern of migration was found for grouper. The limited degree of spawning-related emigration and moderate-high levels of site fidelity indicate that if properly placed, small reserves such as Los Islotes may yet adequately protect small, resident populations of snapper and grouper.</p>

<p> Movement presents a unique challenge for snakes (suborder Serpentes), which utilize limbless locomotion to move in terrestrial and aquatic environments. Lateral undulation, the fastest and most commonly used type of snake locomotion, has been extensively studied in both contexts due to its prevalence in the animal kingdom. However, the effects of speed on locomotor kinematics have only been studied in aquatic conditions. During swimming, snakes are known to increase speed by increasing wavelength and amplitude while maintaining constant frequency. Additionally, amplitude in aquatic environments increases from the anterior to the posterior regions of the body. The mechanism for increasing speed in a terrestrial context is unknown, despite the fact that the majority of snakes reside in terrestrial areas. Therefore, I compared terrestrial locomotor kinematic data with existing aquatic swimming data to determine whether kinematic differences exist for increasing speed in different environments. In this study, Eastern Garter Snakes, <i>Thamnophis sirtalis </i> (<i>n</i>=4), were filmed utilizing lateral undulation at two different speeds with 120fps high-speed video. I examined speed effects on locomotion by conducting detailed comparisons of key kinematic and performance variables including wavelength, amplitude, frequency and segmental angles of the waves created during lateral undulation.</p><p> The speed effects of terrestrial locomotion were found to differ from aquatic locomotor pattern in wavelength; the mean wavelength observed in our terrestrial trials increased significantly as speed increased. Other variables, including frequency, amplitude and growth of amplitude from head to tail, exhibited similar patterns to aquatic locomotion. This study provides insight into the mechanisms by which snakes generate locomotor complexity from a simple body plan.</p>

<p> The widespread introduction of round goby (<i>Neogobius melanostomus </i>) throughout the Great Lakes basin has raised concerns regarding increased risk of egg predation on nesting fish species. Five-minute observation trials were conducted to determine the identity and number of nest predators on rock bass (<i>Ambloplites rupestris</i>), pumpkinseed (<i>Lepomis gibbosus</i>), and smallmouth bass (<i>Micropterus dolomieu</i>) nests following removal of the guarding male. Rock bass had a greater proportion of nests invaded (85.4 %) and average number of predators per nest (9.32, SE 1.7) than pumpkinseed (45.0%, 1.83, SE 0.64) in 2011. Similarly, rock bass had a greater proportion of nests invaded (52.5%) and average number of predators per nest (5.3, SE 1.7) than pumpkinseed (35.0%, 2.3, SE 1.1) and smallmouth bass (37.5%, 2.7, SE 0.94) in 2012. Principal components analysis and canonical correspondence analysis of habitat variables indicates some species are more vulnerable to nest predation due to preferred spawning habitat. </p>