Date of Completion

12-5-2014

Embargo Period

12-4-2014

Keywords

mate-choice, copepods, calanoid, Acartia tonsa, Acartia hudsonica, spermatophore production, reproductive state, body size

Major Advisor

Dr. Hans G. Dam

Associate Advisor

Dr. Ann Bucklin

Associate Advisor

Dr. Stephan Trumbo

Associate Advisor

Dr. George McManus

Field of Study

Oceanography

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

Copepods are the most abundant metazoans in the ocean, link the microbial plankton to upper trophic levels, and affect ecosystem function through their role in biogeochemical cycles. This thesis focuses on an understudied area in copepods-- factors that determine mating success. First, I tested the hypothesis that female-biased adult sex ratios of Acartia tonsa may be explained by ratios already skewed at birth. Offspring of field-caught females were raised to adulthood and the corresponding adult sex ratios were used as proxies for birth ratios. Almost one-fifth of mothers produced significantly female-biased sex ratios, suggesting that secondary processes commonly used to explain sex ratio biases may be less important than hypothesized.

Second, I measured lifetime spermatophore-production rates for males of Acartia tonsa and Acartia hudsonica under high, low, and no food. Spermatophore-production rates and lifetime totals for males of A. tonsa were not affected by food abundance; in A. hudsonica, rates were significantly higher under high food. For both species, there was also a significant decrease in spermatophore-production rates and numbers with age.

Third, I tested whether female mating status affected mate choice in males of Acartia tonsa and Acartia hudsonica. The costs and benefits associated with mating twice versus once for females were also tested. In both species, males mated more frequently with virgin females compared with females that had already mated, suggesting that female reproductive status is important for mating. Frequencies of females carrying double spermatophores in the field were consistently low, implying that mate choice is also present in natural populations. There were no particular costs or benefits to mating a second time.

Fourth, I measured whether variation in encounter time, previous social experience with the same or opposite sex, and food availability influenced the strength of mate choice in Acartia tonsa and Acartia hudsonica. The strength of mate choice between species and among the sexes varied significantly.

Finally, the strength of mate choice was measured over two seasons in field populations of Acartia hudsonica. Mate choice was present in the field, but its strength varied within and between seasons and correlated with a number of ecological factors.

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