Melinda Pickup, Postdoctoral fellow

Department of Ecology and Evolutionary Biology
University of Toronto
25 Willcocks Street
Toronto, Ontario, Canada
M5S 3B2
Phone: (416) 978-5603
Email: melinda.pickup@utoronto.ca

Degrees

  B. Env. Sc. (Honours)

(2000) Department of Biological Sciences/Department of Environmental Sciences, University of Wollongong, Australia.
Thesis title: Reproductive biology and fire ecology of Grevillea rivularis (Proteaceae)
Advisors: Prof. Robert Whelan (UOW) and Dr. Keith McDougall

  Ph. D.

(2008) Department of Botany and Zoology, Australian National University (ANU), Canberra, Australia and Commonwealth Scientific and Industrial Research Organisation (CSIRO) Division of Plant Industry, Canberra, Australia
Thesis title: Local adaptation and outbreeding depression in fragmented populations of Rutidosis leptorrhynchoides (Asteraceae)
Advisors: Prof. Andrew Young (CSIRO) and Prof. David Rowell (ANU)

 

Current Position

Postdoctoral fellow, Professor Barrett's lab,
Department of Ecology and Evolutionary Biology, University of Toronto

 

RESEARCH INTERESTS

 


My research interests are in the evolutionary processes that shape mating systems, adaptation and speciation. I am also interested in the application of, and interaction between, ecological, demographic and genetic processes in species conservation and ecological restoration.

Plant mating systems play a fundamental role in micro-evolutionary processes and macro-evolutionary change and represent a fascinating area of study in evolutionary biology. I am currently a Postdoctoral Fellow in the Ecology and Evolutionary Biology department (EEB) at the University of Toronto, Canada, where I am pursuing research on the mechanisms underlying sex-ratio variation in dioecious species.

Previous research

Local adaptation, outbreeding depression and self-incompatibility in fragmented populations of Rutidosis leptorrhynchoides (Asteraceae)

The primary focus of my Ph.D. was examining local adaptation and outbreeding depression using Rutidosis leptorrhynchoides, a perennial, herbaceous plant distributed across south-eastern Australia. In an evolutionary context, local adaptation and outbreeding depression are central concepts in speciation, adaptive differentiation and the transition from micro to macro-evolution. In addition, for conservation biology, the issues of local adaptation, outbreeding depression and ‘genetic rescue’ are directly relevant to the genetic management of small populations and seed sourcing for revegetation and ecological restoration. A central component of my PhD was experimentally determining the genetic mechanisms underlying outbreeding depression and population divergence. In this project I also examined the potential benefits of introducing new genetic material (through introducing new self-incompatibility alleles) for diploid and tetraploid populations.

Local adaptation was assessed using a transplant experiment that involved 18 population pairs separated by a range of distances from 0.7 – 600 km. For each population pair, seed from both the Target (local) and Source (foreign) populations were planted into soil from the Target population site and grown in a common climate representative of the Target population. Plants were grown for 24 months and the performance of plants from the Target and Source populations were compared for fitness traits across the life-cycle. To examine outbreeding depression, F 1 , F 2 , F 3 and control (within Target population) progeny were generated for 12 of the 18 population pairs using a glasshouse crossing experiment. For the second and third generations, backcrosses to the Target and Source populations were generated to examine the two primary genetic mechanisms underlying outbreeding depression: (i) the dilution of genes associated with local adaptation (admixture analysis), and (ii) the disruption of co-adapted gene complexes through recombination (recombination analysis). F 1 , F 2 , F 3 , backcrosses and control progeny were planted into soil from the Target population sites and, as for the local adaptation experiment, grown in a common climate representative of the Target populations. In this study, I was also interested if measures or surrogates of population divergence, including geographic, environmental or genetic distance between parental populations could predict local adaptation and outbreeding depression. For genetic distance, I examined differentiation for both quantitative traits (Q ST) and microsatellite markers (F ST).

To assess the decrease in fertilization success associated with the loss of S-alleles in small populations of both diploid and tetraploid races, experimental crosses were undertaken for 24 diploid and 5 tetraploid populations. There was a significant decrease in fertilisation success with declining population size for diploid and tetraploid populations of R. leptorrhynchoides, indicating the loss of S alleles in small populations. Fertilisation success increased when crosses were undertaken between populations and this was significantly related to population size for diploid and tetraploid populations, indicating that small populations gain the greatest benefit to fertilisation success from crossing between populations. These results suggest that for small populations that have reduced fertilisation success, genetic rescue by introducing new genetic material from other populations is an important means of ameliorating mate limitation issues associated with reduced S-allele diversity in both diploid and tetraploid races (see Pickup and Young (2008)).

 

Ruditosis leptorrhynchoide
Grassland population of R. leptorrhynchoides

Current research

Understanding the mechanisms underlying sex-ratio variation in dioecious species is a key question in evolutionary biology. Deviations from the expected 1:1 sex ratio maintained by negative frequency-dependent selection (Fisher 1930), indicate either a differential cost in rearing each sex or a difference in the survival of the sexes after parental investment. Although male bias is more common than female bias in dioecious species (Delph 1999), female-biased sex ratios have been reported in species with heteromorphic sex chromosomes (Lloyd 1974), suggesting that sex determination system may influence sex ratios. The two primary hypotheses to explain female-biased sex ratios include; (i) Certation, where gametophytic selection results from differential pollen tube growth of male and female determining microgametophytes (Correns 1922), and (ii) Sex specific mortality, where the sexes show differential growth and/or survival after the period of parental investment (Zarzycki & Rychlewski 1972).

Rumex hastatulus is a wind pollinated, dioecious annual herb distributed throughout mainland North America from Texas north to Illinois, and east through to North Carolina and north to New York. Rumex hastatulus provides an ideal study system to examine the potential role of sex chromosomes in determining variation in sex ratios since it has two distinct cytological races. Populations occurring from North Carolina to Florida and Mississippi (the North Carolina race) are the XX and XY 1Y 2 karyotype (2n = 8 in females and 2n = 9 in males), while population from Louisiana to Texas and Oklahoma (the Texas race) are the XX and XY karyotype (2n = 10 in both sexes). Female biased sex ratios have been observed in the North Carolina race of R. hastatulus (Conn & Blum 1981).

My current research aims to answer the following four questions:

  1. Is there female bias in populations of R. hastatulus?
  2. Are there differences in the patterns of sex-ratio variation between the two chromosome races?
  3. Does maternal mating environment influence female bias? Does this vary between the two chromosome races?
  4. Is there evidence for certation and/or sex specific mortality?
Rumex hastatulus

 

PUBLICATIONS

  • Pickup, M., McDougall, K. L. and Whelan, R. J. (2003) Fire and Flood: soil-stored seed bank and germination ecology in the endangered Carrington Falls Grevillea (Grevillea rivularis, Proteaceae). Austral Ecology 28: 128-136.

  • Pickup, M., Westoby, M. and Basden, A. (2005) Dry mass costs of deploying leaf area in relation to leaf size. Functional Ecology 19: 88-97.

  • Wright, I. J., Falster, D. S., Pickup, M. and Westoby, M. (2006) Cross-species patterns in the coordination between leaf and stem traits, and their implications for plant hydraulics. Physiologia Plantarum 127: 445-456.

  • Pickup, M. and Young, A. G. (2008) Population size, self-incompatibility and genetic rescue in diploid and tetraploid races of Rutidosis leptorrhynchoides (Asteraceae). Heredity 100:268-274.

 

Conference presentations

  • Pickup, M. and Whelan, R. J. Grevillea rivularis: flourishing in the face of fire and flood? Ecological Society of Australia Conference 2000. La Trobe University, Melbourne. Awarded the Trust for Nature Prize awarded for Best Student Oral or Poster Paper on
    “off-reserve” ecological research


  • Pickup, M., Young, A. and Rowell, D. Local adaptation and success of transplanted populations of Rutidosis leptorrhynchoides (Asteraceae). XIX International Congress of Genetics 2003. Melbourne Exhibition and Convention Centre, Melbourne.

  • Pickup, M., Young, A. and Rowell, D. Testing the home-site advantage: Local adaptation and success of transplanted populations of Rutidosis leptorrhynchoides (Asteraceae). Genetics Society of AustralAsia Inc.51 st Annual Conference. University of Melbourne, Melbourne.

  • Pickup, M., Young, A. and Rowell, D. Local adaptation and success of transplanted populations of Rutidosis leptorrhynchoides (Asteraceae) Molecular Biology and Evolution 2005, Auckland, New Zealand. Awarded runners up prize for best student oral presentation

  • Pickup, M., Young, A. and Rowell, D. Genetic Rescue, self-incompatibility alleles and outbreeding depression in fragmented populations of Rutidosis leptorrhynchoides (Asteraceae). European Congress of Conservation Biology 2006. Edger, Hungary. Awarded first place in the Trends in Ecology and Evolution Student Oral Presentation prize at the 2006 European Congress of Conservation Biology, Eger, Hungary.

  • Pickup, M., Young, A. and Rowell, D. Outbreeding depression and population divergence in fragmented populations of Rutidosis leptorrhynchoides (Asteraceae). Evolution 2007. Christchurch, New Zealand.

  • Pickup, M., Young, A. and Rowell, D. How local is local? Outbreeding depression and local adaptation in fragmented populations of Rutidosis leptorrhynchoides (Asteraceae). Ecological Society of Australia 2008. Sydney, Australia.
  • 2006 - First place in the Trends in Ecology and Evolution Student Oral Presentation prize at the 2006 European Congress of Conservation Biology, Eger, Hungary.

  • 2005 - Genetics Society of AustralAsia Student Bursary to attend the 2005 Molecular Biology and Evolution Conference, Auckland, New Zealand.

  • 2005 - Smith –White Travel Award from the Genetics Society of Australia at the Molecular Biology and Evolution Conference 2005 Auckland, New Zealand.

  • 2002 - Australian National University Graduate School PhD Scholarship

  • 2002 - Australian National University Endowment for Excellence Supplementary Scholarship

  • 2002 - CSIRO Postgraduate Scholarship

  • 2000 - The Trust for Nature Prize awarded for Best Student Oral or Poster Paper on “off-reserve” ecological research. Ecological Society of Australia Annual Conference 2000 La Trobe University, Melbourne

  • 1999 - University Medal in the Faculty of Science at the University of Wollongong

  • 1999 - Gina Savage Prize for the best female graduate in Science at the University of Wollongong

  • 1999 - Alan Sefton Memorial Prize for first place in the Environmental Science Program at the University of Wollongong

  • 1998 - 1999 CSIRO Summer Studentship. CSIRO Plant Industry

Teaching experience

  • 2009 - Lecturer for the second year course Evolution and Adaptation, University of Toronto.

  • 2008 - Guest lecturer for the third year course Land and Catchment Management, Centre for Resource and Environmental Studies, Australian National University, Canberra.

  • 2004 – 2007 - Casual Education Officer at the Green Machine Science Education Centre at CSIRO, Black Mountain, Canberra.

  • 2004 – 2005 - Supervisor CSIRO Summer Studentship, CSIRO Plant Industry, Canberra.

  • 2004 – 2005 - Supervisor CSIRO Student Research Scheme, CSIRO Plant Industry, Canberra.

  • 2004 - Demonstrated second year biology Plant Structure and Function in the Department of Botany and Zoology at the Australian National University, Canberra.

  • 2004 - National Youth Science Forum, Canberra.

  • 2000 - Guest lecturer for the third year course Conservation Biology at the University of Wollongong, Wollongong.

  • 1999 – 2000 - Demonstrated first and second year biology at the University of Wollongong. Courses included Evolution, Biodiversity and Environment (first year), Functional Biology of Plants and Animals (second year) and Biodiversity: Classification and Sampling (second year).

References cited

  • Conn , J. S. and Blum, U. 1981. Sex ratio of Rumex hastatulus: The effect of environmental factors and certation. Evolution 35:1108-1116.
  • Correns, C. 1922. Sex determination and numerical proportion of genders in Common Sorrel (Rumex acetosa) (Translated from German). Biol. Zentralblatt 42:465-480.
  • Delph, L. F. 1999. Sexual dimorphism in life history. Pages 149 -174 in M. A. Gerber, T. E. Dawson, and L. F. Delph, editors. Gender and sexual dimorphism in flowering plants. Springer, Berlin, Germany.
  • Fisher, R. A. 1930. The genetical theory of natural selection. Clerendon, Oxford, UK.
  • Lloyd, D. G. 1974. Female-predominant sex-ratios in angiosperms. Heredity 32:35-44.
  • Zarzycki, K., and J. Rychlewski. 1972. Sex ratios in Polish natural populations and in seedling sampling of Rumex acetosa L. and R. thyrsiflorus Fing. Acta Biologica Cracoviensia Series Botanica 15:135-151.