Females increase egg deposition in favour of large males...

Evans, J.P., Box, T.M., Brooshooft, P., Tatler, J.R. & Fitzpatrick, J.L. 2010. Females increase egg deposition in favour of large males in the rainbowfish, Melanotaenia australis. Behavioural Ecology 21:465-469.

Through this study, the researchers address how sexual selection favours flexibility in maternal investment, using rainbowfish as a model species. Females were individually placed into large tanks, with both a small and a large male that were confined to containers within the tank. First, they observed the amount of time the female spent within one body length of the containers containing the males. After four days, either the large or the small male was released into the tank with the female, and they were allowed 4 more days to interact. The eggs produced by the female during this time were collected, counted and photographed. Results showed that during the initial 4 days, females spent 70% of their time within one body length of the large male, and they produced two times as many eggs when they mated with the large male (large males are phenotypically preferred). The variation in maternal investment defined within this study is important for understanding the effect of a mate’s phenotype on maternal investment, but it fails to address the effect of a mate’s genetic identity.

While I continue researching for my thesis project, I’m realizing more and more not to disregard ‘old’ articles just because they are, well, ‘old’. 3 articles by Partridge and colleagues from the 1980s have proven to be of great use to me in understanding costs associated with mating, and how choice influences all individuals in the equation (i.e. males, females and subsequent offspring.) The following are annotations for these articles: 

Fowler, K. & Partridge, L. 1989. A cost of mating in female fruit flies. Nature 228:760-761.

This article looks at the costs a female endures when mating with a male in the model organism Drosophila melanogaster. This is done through mating experiments where virgin females were subjected to either a group of males who all were capable of mating (high-mating) or a group of males where only one of the males was actually capable of mating (low-mating). Males in the low-mating scenario still displayed courting behaviours towards females, but had genitalia removed so they could not actually mate. Results showed that the females who were exposed to high-mating scenarios had significantly lower life spans then those exposed to low-mating. Although this may be a consequence of injury, parasites, or effects of sperm, it still is related to the actual process of mating. These results therefore have profound effects on the future reproduction success of these females. These conclusions are beneficial for me to understand in order to predict then why a female may alter her investment in the subsequent offspring, depending on the costs she has endured through mating.

 Partridge, L. 1980. Mate choice increases a component of offspring fitness. Nature 283:290-291.

In this experiment, larval survival rates are used as a measure of D. melanogasters’ offspring fitness. Males and females are exposed to treatments in which they have the ability to choose mates (cages with many individuals), or where they are unable to choose their mate (randomly selected female exposed to single randomly selected male).  Results show higher fitness in subsequent offspring (i.e. more offspring when exposed to competing larvae) of parents who did have choice in who they mated with, compared to those who did not. The author discusses possibilities of the genetics of these individuals influencing choice, and how if there are differences in paternal and maternal genes, it can lead to fitter offspring because of heterozygosity. This information is relevant to my research, because it is important to understand the how the identity of the parents can have a significant affect on their offsprings’ fitness, especially since the flies in my experiment are exposed to a no-choice treatment.

 

Partridge, L. & Farquhar, M. 1981. Sexual activity reduces lifespan of male fruit flies. Nature 294:580-581.

Partridge and Farquhar study how mating affects the fruit flies’ lifespan by exposing males (Drosophila melanogaster) to different numbers of receptive females and comparing their longevity with control groups. Males in experimental groups were exposed to 1-8 virgin females a day, while males in the control groups were exposed to females who had already been inseminated and therefore would not remate, or with no females at all. Males exposed to the highest number of receptive females (i.e. 8 virgins per day) were shown to have the lowest longevity compared to males who were exposed to fewer receptive females (slightly higher longevity), and control groups (greatest longevity). Understanding the costs associated with mating can help us to understand differences in parental investment of their offspring.

Although these articles are not exactly directly related to my research, the basis of mate choice and affect on all of the individuals involved is very useful background knowledge to have. It allows me to better understand costs of mating behaviours, and hypothesize therefore why differences in parental investment based on the identity of mates may have adaptive benefits.

Long Lab Group Photo October 2012

L:R Conor Delar, Heather McLeod, Erin Sonser, Hannah Tennant, Adam Lounsbury, Maya Ashoka, Sahsa Thomsen (Not pictured: Justine Kraemer or Tristan Long)

Assessing Direct and Indirect Costs

Orteiza, N., Linder, J., & Rice, W. 2005. Sexy sons from re-mating do not recoup the direct costs of harmful male interactions in the Drosophila melanogaster laboratory model system. Journal of Evolutionary Biology, 18(5), 1315-1323.

This article explores how female interactions with males can reduce lifetime survival and fecundity, and assesses any indirect benefits as a result. Virgin females were introduced into two conditions simulating constant male exposure and minimal male interaction. Wild-type males and virgin females are housed and allowed to mate, and then half the females are given the chance to re-mate again with brown eyed males. To determine any direct costs to females by re-mating and constant male exposure females were housed with brown-eyed females and would compete for limited yeast. The costs would then be calculated by recording the eye colour and number offspring each female produced. To assess any indirect benefits virgin females were allowed to mate once with a red-eyed male, and then given the chance to re-mate with a brown-eyed male. The male offspring were then separated according to whether their father was an initially mated or re-mated male and cultured to test for paternity. The study found that the grand-offspring of the re-mated male had slightly lower fecundity than the initially mated male and did not make up for the direct costs involved in re-mating caused by increased male exposure. It is estimated that about 10% of a female’s fecundity is lost through re-mating while about 3% is gained through indirect benefits.

Sex Ratio in Drosophila melanogaster Populations Effect Male Mating Success

Pavkovic-Lucic, S., Kekic, V., & Cvoro, A. 2009. Larger male mating advantage depends on the sex ratio in Drosophila melanogaster. Ethology Ecology & Evolution, 21(2), 155-160.

In this study the mating success of large and small males was examined under specific sex ratios. The mating status of females and males were held constant. Larger males were more successful than smaller males in conditions where the sex ratio was equal, and when there were more males present than females. When more females were present in the population there was no significant difference in mating success of large and small males. In all cases larger males mated earlier, while there was no significant size difference of mated females across the conditions. This is most likely due to the high tracking speeds and increased courtship of larger males. Larger males may have greater mating success than smaller males in male dominated sex ratios because of increased male-male competition. These findings support male-male competition as being an important factor in determining the mating success of larger males rather than a female preference for larger males.

Effects of Male Size on Mating Success and Female Preference in Drosophila melanogaster

Partridge, L., Ewing, A., Chandler, A. 1987. Male Size and Mating Success in Drosophila melanogaster: The Roles of Male and Female Behavior. Animal Behaviour, 35, 555-562. 

In this article the effects of male size in relation to courtship behavior was examined in a non-competitive environment to determine what factors lead to higher courting success in larger males. Male tracking speeds, song frequency and amplitude, as well as frequency of decamping by females was examined. Larger males exhibited louder and more frequent courtship songs as well as faster tracking speeds, while female decamping did not differ significantly among large and small males. This suggests that mating success by larger males is not due to female preference but rather a result of male-male competition. Although the frequency of decamping by the females did not differ, female preference for louder songs and their increased movement as a result of faster tracking speeds by larger males is an important factor in determining female preference for larger males and increased mating success among larger males in a non-competitive environment.

Food Cook!

Gradate Students Hannah Tennant and Adam Lounsbury mixing up a delicious batch of Drosophila banana media (yum!)