First lab-meeting this autumn: on the remarkable diversity and evolution of sex determination systems

Posted by Erik Svensson

After field work and summer break it is time to start up this autumn's lab-meetings again. And what could be more interesting than an article about the remarkable diversity and evolution of sex determination systems? A recently published essay in the journal PLoS Biology, summarizes the current knowledge and state-of-the-art of research in this area. It should hopefully be an interesting read. Below, I attach the Abstract and a link to the paper, which is Open Access and downloadable. The figure above give you a taster about the content. Enjoy!

When: Tuesday, August 12 2014, 10.30

Where: "Argumentet", 2nd floor, Ecology Building.


Sex Determination: Why So Many Ways of Doing It? 

Doris Bachtrog Judith E. Mank, Catherine L. Peichel, Mark Kirkpatrick, Sarah P. Otto, Tia-Lynn Ashman, Matthew W. Hahn, Jun Kitano,Itay Mayrose, Ray Ming, Nicolas Perrin, Laura Ross, Nicole Valenzuela, Jana C. Vamosi, The Tree of Sex Consortium 

Published: July 01, 2014DOI: 10.1371/journal.pbio.1001899 

Abstract

Sexual reproduction is an ancient feature of life on earth, and the familiar X and Y chromosomes in humans and other model species have led to the impression that sex determination mechanisms are old and conserved. In fact, males and females are determined by diverse mechanisms that evolve rapidly in many taxa. Yet this diversity in primary sex-determining signals is coupled with conserved molecular pathways that trigger male or female development. Conflicting selection on different parts of the genome and on the two sexes may drive many of these transitions, but few systems with rapid turnover of sex determination mechanisms have been rigorously studied. Here we survey our current understanding of how and why sex determination evolves in animals and plants and identify important gaps in our knowledge that present exciting research opportunities to characterize the evolutionary forces and molecular pathways underlying the evolution of sex determination.

Everyone loves glowing sperm, right?

Doubly-labelled sperm from Price et al. Nature 400:449-452

Posted by Jessica Abbott on behalf of Katrine Lund-Hansen

Since next week's lab meeting might be the last before summer and field season, I have chosen a paper that should be of interest to all of us. Drosophila, sexual selection, speciation, and glowing sperm.

Title: Postcopulatory Sexual Selection Generates Speciation Phenotypes in Drosophila

Abstract:
Background: Identifying traits that reproductively isolate species, and the selective forces underlying their divergence, is a central goal of evolutionary biology and speciation research. There is growing recognition that postcopulatory sexual selection, which can drive rapid diversification of interacting ejaculate and female reproductive tract traits that mediate sperm competition, may be an engine of speciation. Conspecific sperm precedence (CSP) is a taxonomically widespread form of reproductive isolation, but the selective causes and divergent traits responsible for CSP are poorly understood.
Results: To test the hypothesis that postcopulatory sexual selection can generate reproductive isolation, we expressed GFP or RFP in sperm heads of recently diverged sister species, Drosophila simulans and D. mauritiana, to enable detailed resolution of species-specific sperm precedence mechanisms. Between-species divergence in sperm competition traits and mechanisms prompted six a priori predictions regarding mechanisms of CSP and degree of cross asymmetry in reproductive isolation. We resolved four distinct mechanisms of CSP that were highly consistent with predictions. These comprise interactions between multiple sex-specific traits, including two independent mechanisms by which females exert sophisticated control over sperm fate to favour the conspecific male.
Conclusions: Our results confirm that reproductive isolation can quickly arise from diversifying (allopatric) postcopulatory sexual selection. This experimental approach to ‘‘speciation phenotypes’’ illustrates how knowledge of sperm precedence mechanisms can be used to predict the mechanisms and extent of reproductive isolation between populations and species.

Is "good genes" dead?

Posted by Jessica Abbott

A classic example of sexually selected traits. Picture by Fir0002/Flagstaffotos.

Since we're going to have guests at our next group meeting (see previous post), I thought it might be nice to read a paper about something that all of us have a common interest in: sexual selection. I think this paper has actually come up in conversation a few times during our meetings, but as far as I can tell it's never been chosen as a discussion paper. It's a meta-analysis of sexual selection studies that shows that Fisherian models of sexually selected traits have much better empirical support than good genes theories.

10.30-12.00 on Tuesday May 13th in Argumentet.

Title: Meta-analysis suggests choosy females get sexy sons more than "good genes"
Abstract: Female preferences for specific male phenotypes have been documented across a wide range of animal taxa, including numerous species where males contribute only gametes to offspring production. Yet, selective pressures maintaining such preferences are among the major unknowns of evolutionary biology. Theoretical studies suggest that preferences can evolve if they confer genetic benefits in terms of increased attractiveness of sons (“Fisherian” models) or overall fitness of offspring (“good genes” models). These two types of models predict, respectively, that male attractiveness is heritable and genetically correlated with fitness. In this meta-analysis, we draw general conclusions from over two decades worth of empirical studies testing these predictions (90 studies on 55 species in total). We found evidence for heritability of male attractiveness. However, attractiveness showed no association with traits directly associated with fitness (life-history traits). Interestingly, it did show a positive correlation with physiological traits, which include immunocompetence and condition. In conclusion, our results support “Fisherian” models of preference evolution, while providing equivocal evidence for “good genes.” We pinpoint research directions that should stimulate progress in our understanding of the evolution of female choice.

Visit from Molly Morris and Oscar Rios-Cardenas

Posted by Jessica Abbott

Next week our group will be visited by Molly Morris and Oscar Rios-Cardenas, as part of a STINT-funded collaborative project. They work on the evolution of mating behaviors, animal communication, alternative reproductive tactics and adaptive plasticity in swordtail and platy fishes (Xiphophorus, see picture). The project that we will be working on ties together two of my research interests: reproductive strategy polymorphism and intralocus conflict. We will namely try to investigate whether there is intralocus conflict between alternative reproductive tactics.

You can find our more about Molly and Oscar here:

http://www.ohio.edu/people/morrism/Morris2013/Welcome.html

http://www1.inecol.edu.mx/inecol/personal/rios.htm (in Spanish)

We have also published a paper together on intralocus tactical conflict, which is available here:
http://www.sciencedirect.com/science/article/pii/B9780124071865000070

Mark-recapture manuscript reading.

Hello, For Those Who can come next week, there will be a review of me and Erik's manuscript Comparing mark-recapture methods with traditional methods. 

Tuesday, 10.30. Refreshments will be provided. I will be Distributing the manuscript in the facebook group. 

John Waller

Lab meeting on sexual conflict, sexual selection and mito-nuclear genes

Posted by Anna Nordén

This coming lab meeting (Tuesday April 29^th), we will discuss sexual selection and sexual conflict on the chromosome level. I have chosen a paper that deals with mito-sex chromosome interactions, inter-genomic coadaptation and conflict. Looking forward to some interesting discussions.

Title: The potential role of sexual conflict and sexual selection in shaping the genomic distribution of mito-nuclear genes

Authors: Rebecca Dean, Fabian Zimmer and Judith E. Mank

Abstract: Mitochondrial interactions with the nuclear genome represent one of life’s most important coevolved mutualisms. In many organisms, mitochondria are maternally inherited, and in these cases, co-transmission between the mitochondrial and nuclear genes differs across different parts of the nuclear genome, with genes on the X chromosome having 2/3 probability of co-transmission, compared to 1/2 for genes on autosomes. These asymmetrical inheritance patterns of mitochondria and different parts of the nuclear genome have the potential to put certain gene combinations in inter-genomic coadaptation or conflict. Previous work in mammals found strong evidence that the X chromosome has a dearth of genes that interact with the mitochondria (mito-nuclear genes), suggesting that inter-genomic conflict might drive genes off the X onto the autosomes for their male-beneficial effects. Here, we developed this idea to test co-adaptation and conflict between mito-nuclear gene combinations across phylogenetically independent sex chromosomes on a far broader scale. We found that, in addition to therian mammals, only C. elegans showed an under-representation of mito-nuclear genes on the sex chromosomes. The remaining species studied showed no overall bias in their distribution of mito-nuclear genes. We discuss possible factors other than inter-genomic conflict that might drive the genomic distribution of mito- nuclear genes.

In Argumentet (Ecology Building 2^nd floor) at 11:30 – 12 as usual. I will bring fika!

Lab-meeting: talk about poison dart frogs, predator avoidance and colour polymorphism

 Poison dart frog (Dendrobates pumilo) in Costa Rica 2005 

(Photo: Erik Svensson)

Posted by Erik Svensson

 This coming lab-meeting next week, we will listen to an informal presentation on poison dart frogs and colour polymorphism by visiting student Beatriz Willink, who will soon hopefully join the EXEB-lab as a new PhD-student. Beatriz has done a three-years Master's in Costa Rica, and is an experienced field biologist. Some of Beatriz work has been published in Evolution, Evolutionary Ecology and Behavioural Ecology and Sociobology, and you can follow these links if you want to take a look at her papers.

The title of Beatriz talk is:

"Not everything is black and white: Multiple predators and predator-avoidance strategies in a polytypic poison frog"

 Time and place:

When: Tuesday, April  22, at 10.30
Where: "Darwin Room", 2nd floor, Ecology Building

Any fika volunteer?