BIOL 1111 Chpt 17 Pt 2 Lecture Notes PDF

 Effect of Inbreeding on Genotypes in extreme cases of inbreeding when same genotypes mate to make next generation % of heterozygotes will decline by 50% each generation,...

 Effect of Inbreeding on Genotypes in extreme cases of inbreeding when same genotypes mate to make next generation % of heterozygotes will decline by 50% each generation, whereas homozygotes will increase 25% each generation Fig. 17.14 BUT, from one generation to the next allele frequency does not change Effect of Inbreeding on Genotypes A = 0.5, a = 0.5 (conforms to p2 + 2pq + q2) Mating to produce Generation 1 not random (AA only mate with AA, Aa only mate with Aa, and aa only mate with aa) AA & aa give rise to same genotypes in offspring BUT – Aa x Aa leads to: 50% heterozygotes (Aa) 25% homozygous AA 25% homozygous aa Each generation, % of Fig. 17.14 heterozygotes decreases by 50% (¼ going to each of the AA & aa) and each homozygous goes up 25% Effect of Inbreeding on Genotypes overall, increase in homozygotes (both AA & aa) from one generation to the next & decrease in heterozygotes (Aa) results in deviation from H/W equilibrium (p2 + 2pq + q2) BUT, does not mean evolution occurred…. WHY?: Because allele frequencies do not change from generation to generation Effect of Inbreeding on Genotypes - Inbreeding does not cause evolution because allele freq not changing - Inbreeding simply affects how genotypes are “packaged” into diploid zygotes - Inbreeding does NOT change proportion of alleles in popn, simply moves them from heterozygote to homozygote genotypes - This can lead to inbreeding depression (decrease in average fitness of inbred individuals)  Deleterious alleles tend to be “unmasked” more in an inbred population (more homozygous recessives) Inbreeding This is typically harmful or even lethal depression Can be resolved with outbreeding (genetic rescue) Fig. 17.15 Inbreeding depression in birds Inbreeding depression in humans Inbreeding depression in the wild animals & plants evolve mechanisms to avoid inbreeding mate choice, genetically controlled self-incompatibility, dispersal inbreeding unavoidable in some small populations common problem for rare & endangered species problem for captive breeding programs Inbreeding depression: Florida panther Inbreeding depression: Florida panther Pumas (Puma concolor) are also known as panthers, cougars, mountain lions Pumas are apex predators found in North and South America They provide an interesting case-study of the effects of small populations (inbreeding) Inbreeding depression: Florida panther Panthers were once widespread throughout North America In U.S. and Canada, wild populations are now restricted to the west coast plus Florida Inbreeding depression: Florida panther By the late 20th century, the Florida population had shrunk to 20-25 adults Genetic diversity was rapidly lost Genetic analyses indicated inbreeding within this population Extinction was predicted Using evolutionary principles to save biodiversity Hybridization: mating between individuals of two genetically distinct populations negative effects on biodiversity (e.g. turbidity led to less hybridization among sticklebacks in BC) 2 types: interspecific and intraspecific hybridization Hybrid sink: situation where immigration of locally unfit genotypes produces hybrids with low fitness that reduces local abundance  (ID & OD) (little ID & HV) (OD) Hybrid vigour (heterosis): hybrid offspring Hybridization have higher fitness than either of the parents (or parental organisms) Allendorf et al. (2013) Using a form of hybridization to save biodiversity environmental change, invasive species, overharvesting and habitat loss pose massive threats to biodiversity requires we consider more “aggressive” conservation efforts genetic rescue has been suggested as one such “aggressive” effort to conserve declining populations but it remains controversial Using a form of hybridization to save biodiversity Debate focused on whether the translocated individuals (or alleles) into small populations will lead to increased population by increasing fitness (reduce inbreeding) OR Reduce population fitness via outbreeding depression (reduced fitness of offspring from matings between genetically divergent individuals) Genetic Rescue (GR) GR = increase in population fitness owing to immigration of new alleles reduce extinction risk by increasing absolute fitness – increased population size or growth rate GR causes a population level demographic response to the introduction of new, beneficial alleles via prescribed gene flow  Fitness of individuals of a given phenotype Genetic Rescue indicated via relation between distribution of (cont’d) phenotypes (abundance) and fitness function (broken line) Whiteley et al. (2014) Genetic Rescue (A) represents small imperilled population with reduced phenotypic and genetic variation that (cont’d) could benefit from genetic rescue Whiteley et al. (2014) Genetic Rescue (B) represent successful genetic rescue with an increase in fitness following prescribed gene (cont’d) flow Whiteley et al. (2014)  Dr. S. Fitzpatrick (Michigan State University) Genetic Rescue (cont’d) Genetic Rescue (cont’d) GR used mostly to restore genetic diversity and increasing fitness in SMALL populations these populations are often (but not always) suffering from inbreeding effects inbreeding depression: reduced offspring fitness of offspring from matings between genetically related parents (opposite = outbreeding depression) Genetic Rescue (cont’d) GR does NOT rely on outcrossing large number of individuals, but upon the introgression of beneficial genetic variation from a small number of immigrants WHY?: so that locally adaptive variation is not swamped in theory, low levels of immigration should be enough to decrease frequency of deleterious alleles and provide genetic variation for selection to act on Genetic Rescue Examples Vander Wal et al. (2012) Case Studies premise of the case studies is that population genetic variation will increase with translocation or natural immigration of “small” number of individuals these boosts can be very large when source population is large and the target population is small and inbred few studies have examined fitness effects of low levels of migration across generations Fitness effects most studies (78%, 14/18 studies) showed positive (n=10) or a mix of positive and no of gene flow (n=4) fitness effects Whiteley et al. (2014) Fitness effects CASE STUDIES: (1) Florida Panthers of gene flow (2) Prairie Chickens Whiteley et al. (2014)  Case Studies Florida Panthers Prairie Chickens Johnson et al. 2010 Westemeier et al. 1998 Genetic Rescue Florida Panther Pumas (also called cougars, mountain lions, panthers) endangered Florida panther – last surviving puma subspecies in eastern North America found in shrinking habitats between Miami – Naples 1990s: population of ~24 adults showed low genetic variation (compared to other populations of pumas) that may mean inbreeding (inbreeding depression)  rediscovery of remnant population in FLA prompted genetic rescue program overall, goal was to reduce inbreeding inbreeding can lead to inbreeding depression (which was inevitably leading to extinction vortex)  Florida Panther normal Inbreeding led to: Poor sperm quality Low testosterone levels Low fecundity acrosome defect Poor recruitment Cryptorchidism (80% of males) Kinked tails High load of parasites High level of infectious disease midpiece defect  Florida Panther Inbreeding led to: Poor sperm quality Low testosterone levels Low fecundity Poor recruitment Cryptorchidism (80% of males) Kinked tails High load of parasites High level of infectious disease Florida Panther these observations (along with demographic modelling) predicted 95% chance of extinction in 20yr this set in motion the translocation program in 1995, 8 wild-caught Texas (TX) females pumas moved into habitat where there were 22 Florida panthers Note: historically (before habitat fragmentation) there was gene exchange between Florida and Texas  breeding age panthers shown for 1995 (L) vs 2007 (R) CFP = canonical (last remaining, authentic) FLA panther EVG = everglades FLA panther TX = Taxas panther Johnson et al. (2010)  Minimum annual sub-adult and adult population size CFP = yellow, EVGs = pink, TX = red other colours are “hybrids” and other unknown mixes Johnson et al. (2010)  1996-2003, numbers (N) went up by 14%/year to at least 95 adults 26.6 kittens were produced annually Johnson et al. (2010)  Mean annual multilocus heterozygosity (based on microsats) increase from 18.4% (1993) to 25% (2007) Johnson et al. (2010)  decrease in the mean estimated age of adults from 6.6 years old (1997) to 4.4 years old (2004) population growth slowed and mean age increased after 2004 Johnson et al. (2010)  Admixed ancestry was associated with increased survival of F1 F1 adults had higher survival than CFB groups Johnson et al. (2010)  Johnson et al. (2010) comparison of heterozygosity, cryptorchidism, sperm quality and defects (i.e. atrial septal, kinked tails, cowlick thorax, % abnormal)  Johnson et al. (2010) comparison of heterozygosity, cryptorchidism, sperm quality and defects (i.e. atrial septal, kinked tails, cowlick thorax, % abnormal) e.g. normal sperm: 5.4% for CFP and 20.5% for hybrid  35 year study of a remnant population of greater prairie chickens population decreased from 2000 (circa 1962) to fewer than 50 (circa 1994) fitness (fertility, hatch rates, genetic diversity) decline Westmeier et al. (1998) Prairie Chickens poor reproductive performance and predicted extinction (locally) of Illinois population led to a translocation program in 1992 objectives were to (1) increase numbers and (2) increase genetic diversity and fitness in population between 1992-1996: 271 prairie chickens were transplanted from large populations in Minnesota, Kansas and Nebraska radiotracking data showed that 25-67% of transplanted individuals survived and into breeding population per year and the hatching success (%eggs hatched) increased (see Fig 2)  circles =hatching success triangles = counts of males Westmeier et al. (1998) Experimental Issues? overall, evidence for genetic variation and population growth responses to translocations of individuals immigrant x resident crosses had higher genetic variation (& fitness) that led to demographic increases BUT, studies are unreplicated and uncontrolled studies of single populations (cause/effect difficult) increases in population growth could simply be the result of favourable environmental factors