Form Of Intrasexual Competition Research Articles

Group sex, sex change, and parasitic males: sexual strategies among the fishes and their neurobiological correlates.

Sexual selection, in the form of intrasexual competition and mate choice, has driven the evolution of a variety of sexual phenotypes amongst the vertebrates (Andersson, 1994). As a result, vertebrate species utilize many different approaches to acquire fertilizations. Humans and other primates show a wide range of sexual behaviors, but this range is dwarfed by the remarkable variation seen in advanced fishes. The goals of this review are (a) to acquaint the reader with the tremendous sexual diversity exhibited by fishes, (b) to demonstrate how this diversity provides unique opportunities to examine the neurobiological correlates of vertebrate sexual strategies, and (c) to highlight the parallels between the neuroendocrine correlates of the sexual strategies of fish with the mechanisms underlying sexual phenotypes in other vertebrates, showing the utility of fish studies for understanding sexual variation in general.

Morphological and behavioural correlates of reproductive success in Atlantic cod Gadus morhua

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 354:257-265 (2008) - DOI: https://doi.org/10.3354/meps07175 Morphological and behavioural correlates of reproductive success in Atlantic cod Gadus morhua Sherrylynn Rowe1,*, Jeffrey A. Hutchings2, Jon Egil Skjæraasen3, Louise Bezanson2 1Fisheries and Oceans Canada, Bedford Institute of Oceanography, PO Box 1006, Dartmouth, Nova Scotia B2Y 4A2, Canada 2Department of Biology, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada 3Department of Biology, University of Bergen, 5020 Bergen, Norway *Email: rowes@mar.dfo-mpo.gc.ca ABSTRACT: We tested the hypothesis that reproductive success is randomly distributed within spawning aggregations of Atlantic cod Gadus morhua, a broadcast-spawning marine fish for which no parental care is provided. Based on microsatellite DNA-parentage assignment of 8913 offspring from 4 large (n = 52 to 93) experimental spawning aggregations, we quantified individual variation in male reproductive success and evaluated the degree to which this variation could be explained by aspects of morphology, condition, and spawning behaviour. Reproductive success was highly skewed, with more than 80% of the offspring within each group sired by 2 to 7 individuals. Body size and agonistic interactions initiated were positively associated with male reproductive success within each group. The lengths of fins prominent during courtship and mating were also correlated with reproductive success within one of the spawning groups for which data were available. Our observations are consistent with the hypotheses that some form of intrasexual competition or mate choice is a constituent of the mating system of this species and that the ratio of effective to census population size in broadcast-spawning marine fishes is very small. KEY WORDS: Mating system · Fertilization success · Mating success · Reproductive skew · Broadcast spawning Full text in pdf format PreviousNextCite this article as: Rowe S, Hutchings JA, Skjæraasen JE, Bezanson L (2008) Morphological and behavioural correlates of reproductive success in Atlantic cod Gadus morhua. Mar Ecol Prog Ser 354:257-265. https://doi.org/10.3354/meps07175Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 354. Online publication date: February 07, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Nonrandom mating in a broadcast spawner: mate size influences reproductive success in Atlantic cod (Gadus morhua)

We tested the hypothesis that reproductive success in Atlantic cod (Gadus morhua) is random with respect to similarity in body size between mates. Immediately prior to their natural breeding periods, groups of 52–93 cod from three Northwest Atlantic populations were transported to a large (15 m diameter, 4 m deep) tank where they spawned undisturbed at densities similar to those in nature. Based on microsatellite DNA-parentage assignment of 8913 offspring from four spawning groups, females and males achieved their highest reproductive success when breeding with mates that were larger than themselves. Our observations are consistent with the hypothesis that some form of intrasexual competition or mate choice is a constituent of the mating system of this species and that this can have an important influence on individual fitness. Our results further suggest that reductions in the mean and variance in body size of commercially exploited marine fishes concomitant with size-selective harvesting may have greater negative consequences for population recovery than previously thought.

Male Age Composition and Severity of Conflicts

From a behavioral ecology perspective, all forms of warfare are instances of collective aggression perpetrated predominantly by coalitions of young men. Such coalitions are manifestations of cross-cultural sex differences in aggressive behavior and may be conceptualized as a form of intrasexual competition, occasionally to obtain mates, but more often to acquire resources for the attraction and retention of mates. All societies have young males, yet wars are discrete events that can take place even after long periods of peace. Therefore, an additional factor is needed to explain the episodic nature of the phenomenon. We have proposed (Mesquida and Wiener, 1996) that the most reliable factor in explaining episodes of coalitional aggression is the relative abundance of young males. In this article, we present additional evidence to that effect. The ratio of the number of men ages 15 to 29 years of age versus men 30 and older in a population appears to be associated with the occurrence and severity of conflicts as measured by the number of war casualties. A series of analyses of demographic and war casualty data indicates that the relative prevalence of young men consistently accounts for more than one third of the variance in severity of conflicts.

Copulatory plugs, restricted mating opportunities and reproductive competition among male garter snakes.

REPRODUCTIVE competition for females among males of a given species can take many forms, some of which (like mating plugs) may place constraints on the mating opportunities of males and intensify competition for available females. I have studied the reproductive behaviour of two garter snake species (Thamnophis sirtalis and T. butleri) in the field for 5 years. They do not exhibit pair-bonding, paternal care of offspring, territoriality, or intrasexual combat. Sexual selection in this mating system should favour males which compete to locate, court and mate with the maximum number of females1. Yet I have observed numerous solitary female Thamnophis within the same time periods and areas in which other females were being vigorously courted, often by several males. I have previously observed that the anterior cloaca of any recently mated female Thamnophis contains a copulatory plug which occludes the oviductal orifices2. The plug evidently is formed by the copulating male after sperm transfer. I interpreted this as a form of intrasexual competition in which the successfully copulating male makes the female temporarily unavailable to other males and reduces the likelihood of multiple inseminations. Some reports3,4 indicate that multiple inseminations are possible. I present here evidence from the field that male garter snakes recognise females with a copulatory plug and behave as if these females were unavailable.