Sexual selection, sexual conflict and quantitative genetics

Chief Investigators: Rob Brooks

Sexual selection


Mate choice: In many species, individuals find some members of the opposite sex more attractive as mates. Mate choice can drive the evolution of spectacular and bizarre displays like the colours of male guppies, and the complex calls of male crickets.

Intrasexual interactions: Males may also compete for access to females through combat and scramble interactions. Such competition can select for specialized weapon traits, such as the antlers of male deer, or the elongated heads and legs of some male flies.

Sexually antagonistic coevolution: An important focus of our research is the causes and consequences of conflicts of interest between the sexes. Such conflicts can generate sexually antagonistic coevolution (SAC), or “sexual arms races". SAC is now recognized as a central process in evolution. We are interested in the role of SAC in the maintenance of genetic variation in populations, as well as the relative importance of direct versus indirect selection in male-female coevolution - the question that is at the heart of contemporary research on SAC.

 
Complex mate choice in guppies

There is more than one way to make an attractive guppy. Male guppies court females with an energetic courtship display of their lateral colour patterns. Females also prefer unfamiliar males and males with rare patterns. We use manipulative experiments and multivariate selection analysis to explore the various factors and how they interact to influence choice. We are also using performance physiology to understand the signalling value of the sigmoid display.

 

 

Multivariate fitness surface showing three distinct peaks. Image from Blows, Brooks & Kraft. Evolution 57: 622-630 (2003).

 

 

 

 

 

 

 

PhD student Susi Zajitschek investigating male display and female fecundity in guppies.

 

Experimental aquaria.

Male guppy displaying to a female In characteristic “sigmoid” fashion (Photo: A. Syriatowicz).

Extracting sperm from a female guppy.
 

Cricket calls: multivariate stabilizing selection on sexual display

We use both laboratory and field-based playback and phonotaxis trials to measure the attractiveness of artificially constructed cricket calls. This gives us unprecedented power to detect the true form of selection, and to relate this selection to genetic variation. We have shown that call structure is under strong stabilizing selection and that this stabilizing selection erodes additive genetic variation. We have also shown that sexual selection for greater calling in the field is extremely strong.
 

Field experiment to measure multivariate sexual selection on artificially-constructed calls of the black field cricket Teleogryllus commodus.

 
Human Attractiveness

We are harnessing the power of up-to-the-minute techniques in human animation to conduct manipulative studies of selection on human bodies and faces.

 

Evolutionary quantitative genetics

We seek to understand the genetic basis of phenotypic variation within and among populations, especially in relation to sexually selected traits. Quantitative genetics offers powerful tools to address these questions. By analyzing resemblance between relatives (offspring and parents, full- or half-siblings, cousins) we can gain clues to the genetic basis of traits. We use these tools to study the genetic basis of variation in vertebrate and invertebrate organisms, in order to understand adaptive evolution, and test theory.
 

Four pairs of full brother guppies (red squares), with paternal half sib pairs (in blue) illustrating the strong role of Y-linked genes in guppy colouration.

Longevity in Crickets

Our interest in the relationship between age, longevity and reproductive effort led to four generations of selection on adult male longevity in black field crickets. Male longevity responded rapidly to selection, and greater longevity was associated with reduced nightly and lifetime calling effort. This has led to further quantitative genetic studies of the relationships between reproductive effort in males and females and the potential for conflict between the genes controlling male and female reproduction and longevity to influence ageing.
 

Age-dependent calling effort of male crickets from lines selected for short (solid symbols, solid lines) and long (open symbols, dashed lines) adult male longevity.
Combining Quantitative Genetics with Selection Analysis

By combining our experimental estimates of stabilizing selection on male call properties with quantitative genetic estimates from a half-sib breeding design, we showed that the major axis of genetic variance-covariance matrix (G) is associated with weak selection and the remaining three axes of measured genetic variation are associated with increasingly stronger stabilizing selection.

 

Illustration of the level of genetic variance in relation to the strength of stabilizing selection. Strong stabilizing selection (panels A & B) is associated with relatively little genetic variance (represented by the distribution of breeding values in panel A, blue diamonds). Weaker stabilizing selection (panels C & D) is associated with more genetic variation.

Further reading

Hunt et al., 2006. Artificial selection on male longevity influences age-dependent reproductive effort in the black field cricket. American Naturalist 168: E72-E86.

Zajitschek, F., J. Hunt, S.R.K. Zajitschek, M. D. Jennions and R. Brooks, 2007. No intra-locus sexual conflict over reproductive fitness or ageing in field crickets. PLoS One 155.