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Individual variation in reproductive success in the cooperatively breeding Seychelles warbler

Dr Hannah Dugdale (SoB), Dr Simon Goodman (SoB), Prof David Richardson (U East Anglia), Prof Terry Burke (U Sheffield), Prof Jan Komdeur (U Groningen, NL)

Project partner(s): Nature Seychelles (CASE)

Contact email: h.dugdale@leeds.ac.uk

Accurate measures of fitness components, such as survival and reproduction, are fundamental to the study of evolutionary and conservation biology. However, fitness can be very difficult to measure in natural populations, e.g., individuals may disperse from the study area. Even in closed populations where survival can be monitored accurately, parentage can be hard to assign from behaviour alone, and requires the use of genetic markers. This requires genetic samples, which are usually obtained from offspring soon after hatching/birth. However, measuring fitness at this early life-history stage can be problematic as selection can act at different time points in life, affecting offspring at various ages. Fitness therefore needs to be measured at multiple life-history stages, and extend to grand-offspring, when investigating individual variation in reproductive success. Few studies have done this, as extensive, detailed long-term studies are required. The proposed study will use such data to investigate a range of key factors that impact on individual reproductive success in a cooperatively breeding system of Seychelles warblers (Figure 1). Understanding variation in reproductive success will provide important information to guide the long-term conservation efforts of this once critically endangered species.

 

Figure 1: A Seychelles warbler (Acrocephalus sechellensis; Left, ©Hannah Dugdale) on the study site of Cousin Island, Seychelles (Right, ©Dave Richardson). Individual Seychelles warblers on Cousin are given a unique metal ring on their right leg, with a colour ring on top of it and two colour rings on the left leg that allows unique identification over their lifetimes.

In cooperatively breeding societies, including humans, individuals help to raise offspring that are not their own. Why individuals do this is an intriguing question. In Seychelles warblers, individuals may remain in their natal territory and help to raise offspring, which increases offspring survival. The social environment can therefore impact on fitness. A complication is that helper females may co-breed, and therefore it is important to investigate the direct and indirect fitness benefits of helping, and how the social environment impacts on offspring reproductive success, which this PhD will do.

Another aspect that plays a critical role in determining individual variation in reproductive success is sex. The opportunity for selection provides a measure of this and sets an upper limit to directional selection over one generation. In polygynous mating systems, sexual selection is predicted to be strong. Seychelles warbler groups contain a primary male and female. Females generally produce one egg, which is sired 56% of the time by the primary male, and 44% by a different primary male from a nearby group. The opportunity for selection has not been quantified in this species, and the long-term genetic pedigree will allow investigation of sex effects on reproductive success.

Parental age is also thought to have a strong effect on reproductive success. Individuals experience a decrease in performance in old age, known as senescence. This can have trans-generational effects, such that the offspring of old parents may have reduced fitness compared to offspring that the parents produced when they were younger. Additionally, the project will test whether stressful environmental conditions (Figure 2) affect the strength of the parental age effects on offspring reproductive success.

Figure 2: Photo of the same location in a Seychelles warbler territory in a good season (left), and in a stressful season (right) when monsoonal salt spray defoliates leaves, reducing the insect prey that warblers feed on, from the underside of leaves. ©Janske van de Crommenacker

Both environmental and genetic effects can affect individual variation in reproductive success. It is important to be able to separate these effects as the evolutionary potential of a trait is linked to the amount of its additive genetic variation. Quantitative genetic methods will be employed to separate genetic and environmental effects, and estimate the heritability and evolvability of reproductive success, to provide understanding of the potential for the trait to evolve.

The student will use the exceptional model system of the Seychelles warbler, where individuals are monitored over their entire lifetimes. An existing genetic pedigree of 1,875 birds, spanning 11 generations, will be used to quantify the number of annual, lifetime and grand-offspring. With its uncompromised fitness estimates, detailed environmental data and well understood kin selection effects this dataset provides a unique and powerful resource for studying individual variation in reproductive success.

Objectives:

The successful student will work with researchers at the Universities of Leeds, East Anglia, Sheffield and Groningen to investigate individual variation in reproductive success. The student will address the following fundamental questions in evolutionary and conservation biology:

  1. What is the impact of the social environment on reproductive success?

  2. How does variation in reproductive success differ between the sexes?

  3. How does parental age affect the reproductive success of their offspring?

  4. Is there a genetic basis to reproductive success?

Requirements

You must hold an Honours (2.1 or higher) or Masters degree in a related subject such as Conservation, Biology, Evolution, Genetics, Molecular Ecology, Maths and Biology, or Zoology.

We are looking for a motivated student who has a keen interest in molecular ecology and life-history evolution. Previous experience of bird ringing, fieldwork in harsh environments, molecular techniques, Access databases and statistics would be beneficial; however, the student will receive excellent training in all of these skills. You will be required to conduct fieldwork on the long-term Seychelles warbler project, for a minimum of three seasons (up to 3 months per season).

Training

You will be based within the Ecology and Evolution group, in the School of Biology at the University of Leeds, which is The Times and The Sunday Times University of the Year 2017. You will join Dr Hannah Dugdale’s research group and benefit from co-supervision by Dr Simon Goodman’s Lab. Co-supervision will also be provided by Prof David Richardson (University of East Anglia), and you will be part of the international Seychelles warbler project, which is run in conjunction with Prof Terry Burke (Sheffield), Prof Jan Komdeur (Groningen), and Nature Seychelles. You will benefit from a wide-range of training courses offered by the School of Biology and the Leeds York NERC Doctoral Training Partnership. In particular, this PhD project will provide specialist training in:

  1. Molecular ecology techniques, such as pedigree construction

  2. Fieldwork, on the long-term Seychelles warbler project

  3. Data management, of large datasets stored in an Access database

  4. Statistical analyses, such as generalized linear mixed models applied in a Bayesian framework.

Suggested reading

  • Atema E, Mulder E, Dugdale HL, Briga M, van Noordwijk AJ & Verhulst S. 2015. Heritability of telomere length in the zebra finch. Journal of Ornithology 156: 1113–1123

  • Brouwer L, Richardson DS, & Komdeur J. 2012. Helpers at the nest improve late-life offspring performance: evidence from a long-term study and a cross-foster experiment. PLoS ONE, 7, e33167.

  • Dugdale HL, Nouvellet P, Pope LC, Burke T & Macdonald DW. 2010. Fitness measures in selection analyses: sensitivity to the overall number of offspring produced in a lifetime. Journal of Evolutionary Biology 23: 282–292

  • Hadfield JD, Richardson DS & Burke T. 2006. Towards unbiased parentage assignment: combining genetic, behavioural and spatial data in a Bayesian framework. Molecular Ecology, 15, 3715–3730.

  • Hammers M, Kingma SA, Bebbington K, van de Crommenacker J, Spurgin LG, Richardson DS, Burke T, Dugdale HL & Komduer J. 2015. Senescence in the wild: Insight from a long-term study on Seychelles warblers. Experimental Gerontology 71: 69–79

Related undergraduate subjects:

  • Biology
  • Conservation
  • Evolution
  • Genetics
  • Molecular ecology
  • Zoology