Semester

Spring

Date of Graduation

2006

Document Type

Dissertation

Degree Type

PhD

College

School of Medicine

Department

Physiology, Pharmacology & Neuroscience

Committee Chair

Christy M. Foran.

Abstract

Pipefishes and seahorses of the family Syngnathidae are important inhabitants of diminishing grass beds threatened by excessive nutrient loads, sedimentation, and chemical contaminants. This research examined the influence of these environmental factors on two sympatric pipefishes from the Chincoteague Bay, Virginia. Syngnathids are characterized by a unique mode of reproduction in which the male carries developing embryos in a placenta-like ventral brood pouch until the fry are free-swimming. Interspecific comparisons revealed differences in parental nutrient allocation to embryos. In Syngnathus fuscus, females produce nutritionally poor eggs and males implant developing embryos adjacent to blood vessels. The loose connection between eggs and brood pouch tissues and the appearance of lipid droplets in the pouch of Syngnathus floridae suggest this species utilizes nutrient-rich eggs as nurse eggs to supplement embryonic development. A balanced sex ratio and similar size distributions between the sexes support the physiological evidence of equal parental contribution in S. floridae. In contrast, female-biased breeding populations indicate higher costs of S. fuscus paternity. Because of the potential for lipophilic contaminants to be transferred to developing pipefish through the paternal brood pouch, pipefish are likely to be exposed to contaminants during critical stages of development analogous to in utero human exposure. Following exposure to the PCB mixture Aroclor 1254 over the brood period, we found increased plasma protein and lipid levels in gravid females of both species and S. fuscus males, suggesting altered metabolic demands. Pouch fluid protein and lipid concentrations declined with Aroclor 1254 treatment in S. fuscus but not S. floridae. The first samples from S. fuscus indicate this species is more sensitive to PCB exposure during embryonic development and egg production. Seasonal declines in the concentration of dissolved oxygen, hypoxia, in estuarine waters present a problem of rapidly increasing severity. We investigated pipefish tolerance to hypoxic conditions by monitoring acoustic behavior during feeding. Both species produced high frequency, short duration clicks that positively correlated with food intake. Under hypoxia, reduced feeding activity corresponded with decreased sound production. Overall, these projects compare species responses to environmental stressors to determine how reproductive and feeding behavior relates to species sensitivity.

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