Two NERC PhD studentships (note: you must be a UK citizen to receive NERC funding, however qualified students with independent funding (e.g. though a national funding agency for studies abroad) will also be considered):
Both projects would begin in October 2005
Project 1: Genetic structure of lamprey populations in relation to dispersal and homing.
Background. Lampreys are among the most ancient of extant vertebrates. Many species are anadromous (spawn in freshwater, main growth [ectoparasitic] at sea). This is believed to be an ancestral condition, enabling colonisation of appropriate freshwater habitat as climate has changed. Landlocked populations also occur. Anadromous, parasitic lampreys often form species pairs with non-parasitic, freshwater-resident species. The latter are believed to be derived from the former (Gill et al., 2003), but in the larval stage, species pairs cannot usually be differentiated externally. The associated differences in life history for these two forms should lead to differences in dispersal behaviour and the potential for the evolution of population structure and speciation. In this study the student will test the hypotheses that genetic distance will be greater between populations of Lampetra planeri (wholly freshwater) than for L. fluviatilis (anadromous – river mouth/coastal). However, strong natal homing, as in many salmonids, may limit straying and enhance reproductive isolation and genetic segregation in the anadromous species (Verspoor, 1997). In the salmon model, this involves imprinting on home stream odours and subsequent memory of these cues for home stream orientation (Hasler & Scholz, 1983). Debate remains as to the importance of environmental versus pheromone cues for salmonids, but sea lamprey P. marinus larvae are now known to produce bile acid derived pheromones, to which returning adults are highly sensitive at natural levels (Bjerserlius et al., 2000). Larvae of other lamprey species also produce similar compounds and preliminary work has shown that adult L. fluviatilis is attracted to water containing conspecific odour (Gaudron & Lucas, in review). At spawning, adult P. marinus switch off receptiveness to larval pheromone and adult females are attracted to a sex pheromone produced by males (Li et al., 2002). Yet, contrary to salmon, evidence suggests that P. marinus does not exhibit natal homing (Bergstedt & Seelye, 1995). Thus lampreys provide an extremely good alternative model to salmonids with which to compare the evolutionary relationships between life history, spatial behaviour and genetics. The student will complement their genetic analyses with experimental work towards a better understanding of homing behaviour in L. fluviatilis. We will test the hypotheses that life history is important in determining genetic struction among lamprey species, and that natal homing does not play an important part in the evolution of structure in anadromous species.
Aims. (1) Measure attractiveness of different larval odour sources to adults for conspecifics and heterospecifics (2) Carry out field experiments to study levels of dispersal and reproductive homing in L. fluviatilis; (3) Investigate population genetics among P. marinus and L. fluviatailis populations between sub-catchments and catchments of increasing distance.
Methodology. (1) Adult and larval
lamprey (L. fluviatilis and L. planeri) will be captured
(no licence needed) and brought into the aquarium at Durham. Two-choice
flumes and video will be used to measure attraction of adult lamprey of
different species to conspecific and heterospecific larval odours, as well
as environmental sources of odour, at several dilutions. Larval Lampetra
species will be identified by internal morphology/DNA analysis after behaviour
experiments. Samples of isolated and synthesised pheromone may also be
tested. (2) Telemetry and mark-recapture will be used to study the dispersal
and return migratory behaviour of L. fluviatilis and L. planeri
in the Yorkshire Ouse system. This will be carried out in parallel with
ongoing tracking studies on these rivers and will include translocation
of L. fluviatilis and L. planeri at varying distances from the tributary
to which they have returned, and subsequent assessment of homing to those
sites. (3) Non-destructive tissue samples from up to six putative populations
(typically about 50 samples per population) of the two species will be
analysed using microsatellite DNA loci, for analysis of population genetic
variation and to assign L. fluviatilis and L. planeri larvae to species
using likelihood methods. Populations will be compared using both
standard F-statistics and likelihood assignment methods. Gene flow
estimates will be derived using coalescent methods. Samples of both
species have been obtained from a range of spatial scales from minor tributaries
within the same catchment, to major catchments overseas. Supervision
will be provided by Rus Hoelzel & Martyn Lucas
Project 2: Extra-pair paternities and genomic correlates to lifetime reproductive success in the tawny owl
The tawny owl (Strix aluco) is the most common and widespread owl in Europe. They are primarily found in broadleaved woodland, but have adapted well to a range of man-altered habitats. Food supply is one of the most important factors influencing the demography and distribution of raptors in general, and tawny owls are no exception. Their life history is shaped by rodent populations that vary in abundance from year to year. In the study area at Kielder Forest, their most important prey are field voles (Microtus agrestis). At Kielder, vole populations exhibit cyclic dynamics with peak numbers occurring every 3-4 years. Tawny owls are highly philopatric and overcome years with few voles by ceasing to breed and by utilising alternative prey, such a common frogs and birds.
For this study we have access to blood samples from 781 owls collected over a period from 1994 to 1998 (encompassing a complete vole cycle with peaks in 1994 and 1998 and a nadir in 1996). This includes 171 nesting pairs and their offspring, and the sampling within the forest was nearly inclusive of all breeding attempts for most years. This gives us the opportunity to determine parentage using genetic markers, and since we have samples from most nests for most years, we can assess the proportion of extra pair copulations (EPC). We also have life-time reproductive success data for approximately 60 owls. Taken together, these data allow us to assess reproductive strategy and success in the context of a cyclic environment, where prey availability declines at regular intervals. This dataset is essentially unprecedented in its completeness for any raptor species.
EPC occurs in many avian species with a wide range of frequencies. For example, it’s very rare in the fulmar (Fulmarus glacialis), but in reed buntings (Emberiza schoeniclus) 86% of nests contain extra-pair young. This broad range of incidence is even seen within genera, for example comparing the aquatic warbler (Acrocephalus paludicola; 36% of offspring extra pair) with the great reed warbler (A. arundinaceus; 3.4% of offspring extra pair), and within species. For willow warblers (Phylloscopus trochilus), one study found no EPCs while another found evidence for EPCs in 50% of the nests. There can also be temporal variation in this pattern, for example in the red-winged blackbird (Agelaius phoeniceus) where the proportion of EPC varied from 17% to 35% over a 5-year study (see review by Petrie & Kempenaers (1998)TREE 13:52-58).
In most bird species it is the female who can control the success of copulations and the transfer of sperm, though males have sometimes evolved counter-strategies. Therefore, EPC frequency may depend primarily on variation in the benefits and costs to females, and on constraints on female choice. Many of the ideas about likely benefit to females focus on increasing the genetic diversity of their offspring or seeking ‘good genes’. Some speculate that the female should therefore be more disposed to allowing EPC when population genetic diversity is high, though it is unclear how a female would assess this. Environmental factors, however, could be assessed more directly. When environmental conditions are difficult (e.g. resources limited), the most fit males may be those who can achieve multiple matings. Allowing EPC when resources are limited may also help protect a female against mate loss and to gain direct benefit from a neighbour’s territory (as has been reported for red-winged blackbirds). Males may also want to increase EPC when resources are limiting to bet-hedge against the loss of offspring at any given nest.
Tawny owls reduce or stop breeding altogether when the vole cycle is at its nadir, however the optimal strategy may involve increasing EPC during the downward phase of the vole cycle, in anticipation of the harsher conditions, and decreasing EPC during the upward phase of the cycle. This hypothesis will be tested from the combined field and genetic paternity data available for this study. Given complete data on reproductive success, including extra-pair reproductive success, we can compare individuals for long-term, and for 60 individuals, lifetime reproductive success.
All owls in the study have been measured for characteristics that could contribute to fitness, such as indicators of body size & condition. Further, the data used to assess paternity (microsatellite DNA genotypes) can be used to assess genomic diversity, and this has been shown in a number of studies to correlate to reproductive fitness (e.g. in the red deer, Cervus elephus, Slate et al. (2000) Proc. Royal Soc. B 267:1657-1662). Therefore, a second hypothesis to be tested will be that individual reproductive success is correlated to individual fitness, either in terms of physical characteristics, or genomic diversity (as an indicator of inbreeding).
Paternities will be determined using published microsatellite DNA loci, already shown to provide sufficiently polymorphic markers for paternity determination in this species. All samples are currently stored in Durham, and the student would begin with the DNA extraction, followed by microsatellite DNA genotyping, paternity determination using standard software (available in the lab), and interpretation.
The student should have a strong background in molecular ecology, behavioural ecology, evolution or related studies. Supervision will be provided by Rus Hoelzel and Chris Thomas.
Applications:
Applications should include two letters of reference, A-level grades, grades to date in undergraduate degree programs, expected degree outcome (or outcome if known), a cover letter explaining your interest in the project and your research interests in general (please specify which project you would like to be considered for), and a copy of your c.v.
Post or email material to:
A. Rus Hoelzel
School of Biological and Biomedical Sciences
Durham University
South Road, Durham
DH1 3LE, UK
a.r.hoelzel@dur.ac.uk
Note: Application deadline is 1 March 2005
Lampetra planeri photo from http://www.ittiofauna.org/. Tawny Owl photo by C.J. Thomas.