Authors
  • Hanson, Kyle C.
  • Cooke, Steven J.
Universities

Summary

In female mate choice, a female chooses a reproductive partner based on direct or indirect benefits to the female. While sexual selection theory regarding female mate choice is well developed, there are few mechanistic studies of the process by which females evaluate reproductive partners. Using paternal‐care‐providing smallmouth bass (Micropterus dolomieu) as a model, the purpose of this study was to determine the relationship between female mate choice and the morphological and physiological status of chosen males. This was accomplished by locating nests within 1 d of spawning and categorizing brood size (indicator of female mate choice). This was followed by capture of parental males, which were blood sampled (for nutritional analyses), digitally photographed (for morphometric analyses), and released. Principal components analysis (PCA) of morphometric measurements described 72.7% of the variance associated with body morphology and generated three principal components (PCs) indicative of fusiform body shape, increased posterior size, and body stoutness. PCA of nutritional indicators described 75.4% of the variance associated with physiological metrics and generated two PCs indicative of plasma mineral content (Ca++ and Mg+) and energetic condition (total protein, triglyceride, and cholesterol). Male total length and body stoutness were the only significant predictors of female mate choice. Interestingly, no nutritional indicators were predictive of female mate choice, and there were no direct relationships between morphological variables and nutritional physiology indicators. Further research is needed to elucidate the mechanistic relationships between morphology and nutritional physiology (especially in relation to the parental‐care period) of individual fish to determine the basis of female mate preference.

Methodology

This study was carried out from May 24 to June 5, 2007, on Charleston Lake, eastern Ontario, Canada (44°32'14"N, 75°59'48"W). To eliminate confounding factors associated with a trend in which larger males spawn earlier during the spawning period (typically lasting 3 wk [Wiegmann et al. 1992; Kubacki et al. 2002]), all sampling of males was conducted during the first 3 d of spawning in a lake where we had previously observed a wide range of size among parental males even early in the spawning period. At the beginning of every sampling day (May 24–26), snorkel surveys of the littoral zone (typically less than 1-m water depth) were conducted to locate smallmouth bass that were actively guarding nests with newly deposited eggs (1 or 2 d old). Upon locating an active bass nest, the snorkeler placed a numbered polyvinyl chloride tile near the nest and recorded nest location, nest depth, and number of eggs within the nest (visual, categorical assessment ranging from low of 1 to high of 5; Suski and Philipp 2004). Fish were then captured using heavy-action recreational fishing equipment that could be used to angle fish from the boat or underwater (by the diver). All fish were landed within 20 sec of hooking to minimize nonparental-care-related anaerobic exercise. Upon capture, fish were placed supine in a foam-lined sampling trough filled with fresh lake water and quickly blood sampled by the caudal puncture method using a 1.5-inch, 21-gauge vacutainer syringe (Houston 1990). Approximately 1.5 mL of blood was collected in a 3-mL vacutainer containing lithium heparin to prevent blood coagulation and was then placed into a waterice slurry. Additionally, total length was measured, and presence or absence of injury was noted. Individuals were transferred to a flat, foam-lined, spatially referenced tray and digitally photographed (Pentax Optio WPI, 6 megapixel, Pentax Imaging, Golden, CO) from 0.60 m directly above. Individuals were then released within 5 m of the nest. During the sampling procedure (191 ± 5 s), a snorkeler remained at the nest site and defended the brood until the male returned (typically in under 5 min). In total, 86 male bass were sampled. Blood samples were centrifuged (after sampling six fish) at 10,000 g for 5 min (Clay Adams Compact II Centrifuge), and plasma samples were stored in liquid nitrogen for subsequent analysis. Snorkel surveys to determine presence or absence of the male were conducted 7 and 10 d after sampling, which roughly corresponded to the end of the larval stage of brood development. Presence of the male on the nest at this time was used as a measure of parental-care success because after the eggs hatch, parental males provide less vigilant parental care and are more prone to abandon the nest as the brood becomes increasingly independent (Sargent and Gross 1986; Ridgway 1988; Cooke et al. 2002).

Location