Measuring inbreeding Measuring inbreeding Connection to population - PowerPoint PPT Presentation

Causes of inbreeding depression Read Chapter 11 (pp 376-399) Reduced heterozygosity Alter, S. E., Rynes, E. and Palumbi, S. R. (2007) Increased exposure of recessive deleterious alleles in DNA evidence for historic population size and homozygotes What is inbreeding? past ecosystem impacts of gray whales. PNAS Recessive deleterious alleles are common in large What is inbreeding depression? 104: 15162–15167 populations. These alleles are at low frequencies and typically occur mainly in heterozygotes and are therefore Why are small populations a problem? not purged from the populations because there is no What is Mutation - Drift balance? associated penalty for the heterozygotes. In small populations, just by chance, they might get fixed Measuring inbreeding Measuring inbreeding Connection to population size for population we use the heterozygosity as a proxy t = number of generations F = H Expected − H observed 1 F = H e − H o ) t F = 1 − (1 − 2 N e H Expected H e F measures the deviation from a Homozygosity if Hois zero, F is maximal and 1 random mating population Probability that variability is maintained over t generations Inbreeding coefficient if Ho is equal to He, F is 0 using Hardy-Weinberg proportions and H Expected = 2 pq two alleles

Connection to population size Connection to population size N e = 100 F 1 1 ) t ) t F = 1 − (1 − F = 1 − (1 − 2 N e 2 N e N e = 1000 N e = 10 , 000 F N e F N e N e = 100 , 000 Time t F t F t Predicting inbreeding depression Extinction vortex Clarkia – a naturally self-pollinating plant that does not show inbreeding depression EXTINCTION The frequency of Hedrick, P. W. 2001. Conservation Genetics: where are we now? Trends in Ecology and Evolution 16:629-636 matings between close relative rises What is the chance of suffering INBREEDING Scenario Genetic load “Inbreeding depression” when mating with close relatives Population High becomes smaller Large population Low “the worse it gets, (large number of rare Heterozygosity is reduced in semilethal alleles) offspring, reducing the ability to the worse it gets.” respond to environmental change Intermediate Intermediate Recently small (purged some detrimentals of (fixed some detrimentals with population Caughley 1994 large effect) small effect) Low High Long-term small (purged detrimentals of (fixed many detrimentals with As a result of this expression, population medium or large effect) small effect) fecundity is reduced and Semilethal recessive alleles are mortality is increased expressed in homozygous Genetic load = Reduction of the mean fitness resulting from detrimental variation for a population (inbreeding depression) conditions compared to a population without lowered fitness.

Colonial naked mole rats do not show much inbreeding depression Heredity (1996) 76, 83–91; doi:10.1038/hdy.1996.11 VIRAL EPIZOOTIC REVEALS INBREEDING DEPRESSION IN A HABITUALLY INBREEDING Variation in inbreeding depression among families and populations of Clarkia MAMMAL tembloriensis (Onagraceae) Adin Ross-Gillespie 1,2,3 , M. Justin O'Riain 1 , and Lukas F. Keller 4 1 Department of Zoology, University of Cape Town, Rondebosch 7700, South Africa 2 E-mail: A.Ross-Gillespie@ed.ac.uk 4 Zoologisches Museum, Universität Zürich, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland Timothy P Holtsford 1 Correspondence to 3 Present address: Institute of Evolutionary Biology, University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, 1 Division of Biological Sciences, University of Missouri, Columbia, MO 65203, USA United Kingdom. Associate Editor: H. Kokko Received 9 June 1995. Correspondence to 3 Present address: Institute of Evolutionary Biology, University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, United Kingdom. Top of page Abstract KEYWORDS The relationship between the self-fertilization rate of a population and the severity of inbreeding Coronavirus • disease susceptibility • Heterocephalus glaber • inbreeding depression • purging ABSTRACT depression is difficult to predict because the underlying genetics may be complex. However, it is important to understand this relationship, and the degree to which inbreeding depression varies Inbreeding is typically detrimental to fitness. However, some animal populations are reported to inbreed without incurring inbreeding among families within populations, if we are to understand the evolution of plant mating systems. depression, ostensibly due to past "purging" of deleterious alleles. Challenging this is the position that purging can, at best, only adapt a population to a particular environment; novel selective regimes will always uncover additional inbreeding load. We consider this in a Inbreeding depression was studied in glasshouse trials using seed derived from two populations of prominent test case: the eusocial naked mole-rat ( Heterocephalus glaber ), one of the most inbred of all free-living mammals. We Clarkia tembloriensis , Cantua Creek and Idria. These had very different rates of self-fertilization (s) investigated factors affecting mortality in a population of naked mole-rats struck by a spontaneous, lethal coronavirus outbreak. In a and inbreeding coefficients (F) (s = 0.74, F = 0.77 in the CC-1 population; 5 = 0.16, F = 0.10 in the multivariate model, inbreeding coefficient strongly predicted mortality, with closely inbred mole-rats ( F � 0.25) over 300% more likely to die I-1 population). Outcrossing between these populations was equivalent to outcrossing within them; than their outbred counterparts. We demonstrate that, contrary to common assertions, strong inbreeding depression is evident in this there was no evidence for outbreeding depression or increased heterosis from interpopulation species. Our results suggest that loss of genetic diversity through inbreeding may render populations vulnerable to local extinction from crosses. The more self-fertilizing CC-1 population had fewer recessive lethal genes than the emerging infectious diseases even when other inbreeding depression symptoms are absent. outbreeding I-1 population. However, cumulative inbreeding depression at the end of flowering was not significantly different between these populations. Inbreeding has seemingly purged the lethal Received January 29, 2007 genes from the CC-1 population but overall mutational load, especially in characters that are manifest late in the life history, is still substantial despite a history of inbreeding. Variation in Accepted May 8, 2007 inbreeding depression among families within these two populations was surprisingly large. The range DIGITAL OBJECT IDENTIFIER (DOI) of variation among families was five to seven times larger than the difference in inbreeding 10.1111/j.1558-5646.2007.00177.x depression between populations. Variation in inbreeding depression among families should make these populations more susceptible to the invasion of genes which increase the rate of self- fertilization. Keywords: Clarkia , inbreeding depression, mating system, self-fertilization Larkspur Inbreeding avoidance Predicting inbreeding depression Delphinium nuttallianum Plants Self-incompatiblity Hedrick, P. W. 2001. Conservation Genetics: where are we now? Trends in Ecology and Evolution 16:629-636 What is the chance of suffering Male and female parts flower at different times “Inbreeding depression” when Scenario Genetic load Distance between Overall fitness mating with close relatives Heterostyly (females and male parts are far from each parents (m) other) 0.30 a 1 High Male and females are different plants Large population Low (large number of rare 0.42 b 3 semilethal alleles) Animals Intermediate Intermediate Mate choice (mice smell whether they belong to the same 10 0.65 b Recently small (purged some detrimentals of (fixed some detrimentals with MHC type or not) population large effect) small effect) 0.08 a 30 Migration behavior (Young lions get driven from their Low High Long-term small pack) (purged detrimentals of (fixed many detrimentals with population medium or large effect) small effect) Genetic load = Reduction of the mean fitness resulting from detrimental variation for a population compared to a population without lowered fitness.