Tuesday, October 23, 2012

Male genotype influences female reproductive investment in Drosophila melanogaster

Pischedda, A., Stewart, A.D., Little, M.K. & Rice, W. 2011. Male genotype influences female reproductive investment in Drosophila melanogaster. Proc Biol Sci 278:2165-72.

This study is the first form of direct evidence that males vary genetically in their influences on female fecundity, egg sizes and overall female investment in reproduction. Female Drosophila melanogasters were mated with males from 10 different ‘worldwide lines’ (to account for genetic variation) for 2 hours. After this time, females were placed into individual oviposition vials for 22 hours, followed by transfer into a new oviposition vial for another 22 hours. After that, all of the females who mated with males from the same worldwide line were put into the same egg laying chamber and allowed 4 hours to oviposition. Eggs from the chamber were then photographed and measured. Results found that a male’s population of origin did not affect egg size, but did affect females' fecundity in the first 22 hours after mating. The genotype of the males within a population did however account for some of the variation seen in egg size. This study is very useful to me, as it relates directly to the question at the forefront of my research. It does not however address the mechanisms causing the variations seen, such as female cryptic choice or manipulations by males, so leaves room for further investigation and analysis. 

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.

Friday, October 5, 2012

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)