On crypsis in South African leafhoppers on May 29 (2013)

Posted by Erik Svensson

Apart from our regular lab-meeting now on Tuesday (May 28), I would also like to announce a thesis-defence (BcSci; 30 points) by one of our students: Johanna Eklund. Her presentation will take place on Wednesday May 29 at 15.00 in "Argumentet". 

Opponent will be Associate Professor Marie Dacke from "The Vision group". The title of Johannas project is:

"Crypsis through the eyes of a predator"

Johanna has been studying camouflage in leafhoppers (Homoptera) in South Africa at Stellenbosch University, as part of my research exchange grant funded by SIDA/VR. This should be very interesting, whether you are interested in predator-mediated selection, colour evolution and ecology, visual ecology or all of these fascinating topics.

Everybody should be most welcome!

Asexuals, Speciation, and Population size

Can you keep being an asexual without risk of extinction if your population size is large enough? Let's discuss at next lab meeting.


"LARGE POPULATION SIZE PREDICTS THE DISTRIBUTION OF ASEXUALITY IN SCALE INSECTS"

Abstract
Understanding why some organisms reproduce by sexual reproduction while others can reproduce asexually remains an important unsolved problem in evolutionary biology. Simple demography suggests that asexuals should outcompete sexually reproducing organisms, because of their higher intrinsic rate of increase. However, the majority of multicellular organisms have sexual reproduction. The widely accepted explanation for this apparent contradiction is that asexual lineages have a higher extinction rate. A number of models have indicated that population size might play a crucial role in the evolution of asexuality. The strength of processes that lead to extinction of asexual species is reduced when population sizes get very large, so that the long-term advantage of sexual over asexual reproduction may become negligible. Here, we use a comparative approach using scale insects (Coccoidea, Hemiptera) to show that asexuality is indeed more common in species with larger population density and geographic distribution and we also show that asexual species tend to be more polyphagous. We discuss the implication of our findings for previously observed patterns of asexuality in agricultural pests.
10.30 Darwin
Fika Provided

The evolution of male mate choice

Posted by Jessica Abbott

At the last group meeting we got to talking about male mate choice, and what factors could favour the evolution of male mate choice.  To follow up on this, I thought it would be interesting to read a relatively recent paper by Sandra South, Göran Arnqvist, and Maria Servedio on this topic.  It's a model that shows that female preference for male courtship can drive the evolution of male mate choice, and was inspired by Sandra's results on the mosquito species she studied during her PhD.

Sabethes cyaneus, a species in which both sexes have ornaments.  Photo by Sandra South.

FEMALE PREFERENCE FOR MALE COURTSHIP EFFORT CAN DRIVE THE EVOLUTION OF MALE MATE CHOICE

Sandra H. South, Göran Arnqvist, Maria R. Servedio


Evolution
Volume 66, Issue 12, pages 3722–3735, December 2012

The evolution of male mate choice is constrained by costs of choice in species with a male-biased operational sex ratio (OSR). Previous theoretical studies have shown that significant benefits of male choice are required, for example, by mating with more fecund females, in order for these costs to be offset and a male preference to spread. In a series of population genetic models we show the novel effect that male mating preference, expressed as a bias in courtship, can spread when females prefer, and thus are more likely to mate with, males who court more. We explore two female preference functions for levels of male courtship, one representing a threshold and the other a weighted female preference. The basic finding generally holds for both preference functions. However, the preference function greatly affects the spread of a male preference allele after the addition of competing males who can court more in total. Our results thus stress that a thorough understanding of the response of females to male courtship is a critical component to understanding male preference evolution in polygynous species.

Bateman in Nature

#posted by Maren Wellenreuther

Dear all,
next week we will revisit a paper in Science that we discussed in a previous lab meeting this year: Bateman in Nature: Predation on Offspring Reduces the Potential for Sexual Selection by John Byers and Stacey Dunn. In the paper the authors state 'We found no evidence that random effects skewed male mating success; however, substantial yearly variation in the Bateman slope due to predation on fawns was evident. These results support the validity of the Bateman relationship, yet they also demonstrate that environmental or extrinsic influences can limit the potential for sexual selection'. 

 
Fly guy: Angus John Bateman used Drosophila to study the benefits of promiscuity.

This month a comment was published in Science and three key criticisms against the paper are raised 1) their nonstandard calculation of Bateman slopes;
2) their assertion that random processes do not influence reproductive success;
3) and the statistically unjustifiable use of 6 variables to explain just 10 observations.

Erik also suggested some additional reading, namely a TREE paper by Schaerer, Rowe and Arnquist about Anisogamy, chance and the evolution of sex roles


Lets talk about Batemans principles and related issues in greater depth at the next lab meeting, May the 14th 10:30 at Argumentet. I will bring some fika. 

Below are the two abstracts

Comment on “Bateman in Nature: Predation on Offspring Reduces the Potential for Sexual Selection”
Steven A. Ramm, Rudy M. Jonker, Klaus Reinhold, Tamás Székely, Fritz Trillmich,Tim Schmoll, Holger Schielzeth and Robert P. Freckleton
Byers and Dunn’s (Reports, 9 November 2012, p.802) conclusion that predation constrains sexual selection is problematic for three reasons: their nonstandard calculation of Bateman slopes; their assertion that random processes do not influence reproductive success; and the statistically unjustifiable use of 6 variables to explain just 10 observations.

Anisogamy, chance and the evolution of sex roles
Lukas Schärer,Locke Rowe and Göran Arnqvist
Recently, several authors have challenged the view that anisogamy, the defining feature of the sexes, is an important determinant of the evolution of sex roles. Sex roles are instead suggested to result from chance, or from non-heritable differences in life histories of females and males. Here, we take issue with these ideas. We note that random processes alone cannot cause consistent differences between the sexes, and that those differences between the sexes in life histories that affect the sex roles are themselves the result of sex-specific selection that can ultimately be traced back to anisogamy. To understand sex roles, one should ask how environmental variation and female–male coevolution cause variation in sex-specific selection in the light of anisogamy.

Next Week’s Lab Meeting: WIPs and Study of Color Patterns

Male displaying wing during courtship.

For the next week I’ll give a presentation on the work of fruit fly WIPs I’ve been doing. Also Anais and I will show you the video footage of male mating preference on both wild type LHm and Androchrome females. Hope to hear your thoughts and advises.

To continue with the theme of WIPs, I think we can read this paper Erik suggested earlier about the new tool for studying animal colour patterns and the possible application on our studies. Fika will be served!

Title: Distance transform: a tool for the study of animal colour patterns

Summary:

1. The information in animal colour patterns plays a key role in many ecological interactions; quanitification would help us to study them, but this is problematic. Comparing patterns using human judgement is subjective and inconsistent. Traditional shape analysis is unsuitable as patterns do not usually contain conserved landmarks. Alternative statistical approaches also have weaknesses, particularly as they are generally based on summary measures that discard most or all of the spatial information in a pattern.

2. We present a method for quantifying the similarity of a pair of patterns based on the distance transform of a binary image. The method compares the whole pattern, pixel by pixel, while being robust to small spatial variations among images.

3. We demonstrate the utility of the distance transform method using three ecological examples. We generate a measure of mimetic accuracy between hoverflies (Diptera: Syrphidae) and wasps (Hymenoptera) based on abdominal pattern, and show that this correlates strongly with the perception of a model predator (humans). We calculate similarity values within a group of mimetic butterflies and compare this with proposed pairings of Müllerian comimics.

4. Finally, we characterise variation in clypeal badges of a paper wasp (Polistes dominula) and compare this with previous measures of variation.

While our results generally support the findings of existing studies that have used simpler ad hoc methods for measuring differences among patterns, our method is able to detect more subtle variation and hence reveal previously overlooked trends.

Qinyang