INBREEDING IN SOCIAL ANIMAL SYSTEMS. Sam Straus Avilés Lab (Zoology) BIOL 509

Transcription

1 INBREEDING IN SOCIAL ANIMAL SYSTEMS Sam Straus Avilés Lab (Zoology) BIOL 509

2 Overview Why might inbreeding be advantageous? Mathematical models Inbreeding causes and effects Examples of inbred social systems

3 Inbreeding Avoidance Mechanisms Discrimination against mating with kin Dispersal Negative frequency dependent selection

4 Terms defined δ à inbreeding depression r à degree of relatedness c à costs of avoiding inbreeding (i.e. cost of dispersal)

5 Dispersal Sex bias for inbreeding-driven dispersal ex. Female birds disperse, male mammals disperse (Greenwood 1980, 1983) In polygynous mating systems, females prefer immigrants males if δ > r 1 + r Females prefer related males if δ < r 1 + r

6 More Mathematical Models Monogamous mating system (Waser 1986) Inbreeding favored if δ < c Polygynous mating system For females, inbreeding favored if δ < r + c 1 + r For males, inbreeding favored if δ < 1 + rc 1 + r Figure from Avilés and Purcell 2012

7 Common Characteristics - Causes Limited dispersal abilities = High cost Patchy environment Physiology Small body size Reduced or absent wings Patchy distribution Figure from Avilés and Purcell 2012

8 Common Characteristics - Effects Highly biased female:male sex ratios Haplo-diploidy Outbred lineages more diverse than inbred lineages Reduced selfish behavior in individuals (Hamilton 1972)

9 Altruism and Relatedness Hamilton one of the first to describe altruism as a function of relatedness rb > C B à Reproductive benefit to recipient of an altruistic act C à Reproductive cost to individual performing altruistic act

10 Altruism and Relatedness Would I jump in a lake To save my drowning cousin? It's not a risk I'd take For him plus half a dozen. But if you raise the stake And make the prize my brother? Now that's a deal I'll make... If you'll just toss in another. Family Values from Queller 2001

11 Vertebrate Example: Naked Mole Rats Eusocial, Diplo-diploidy Compare to Damaraland Mole Rat Outbred system Larger bodies, less patchy environment 8% reproduction vs. 0.01% Photo cr. Frans Lanting

12 Naked Mole Rats One study found F = 0.45 (Reeve 1990) Strong inbreeding depression When F > 0.25, 300% more likely to die (Ross-Gillespie 2007) Highly inbred populations vulnerable to extinction Large litter sizes might help counteract the effects 1998) (Stockley and Macdonald

13 Vertebrate Example: Prehistoric Humans Evidence of inbreeding in Pleistocene Homo (Wu 2012) Excavations of prehistoric remains in 1977 Skull deformities à inbreeding Not lethal Caused by demographic instability Photo from Wu 2012

14 Invertebrate Example: Parasitic Ants Eusocial, Haplo-diploidy Founder queens hijack host nest Breed within the nest Highly female biased sex ratios as a result of inbreeding (Buschinger 1989) Myrmoxenussp. Photo cr. Wikimedia Commons

15 Parasitic Ants Reduced wings AND small body sizes High cost of dispersal Inbreeding depression in Cardiocondyla obscurior (Schrempf et al. 2006) Reduced male sperm counts Shorter female lifespan

16 Invertebrate Example: Termites Eusocial, Diplo-diploidy Inbreeding à rapid colony growth (Shellman- Reeve 1997) Highly inbred WITHIN colonies Inbreeding depression can be high (Calleri et al. 2006) Higher loads of pathogenic microbes Fungal infections Photo cr. CSIRO

17 Termites Reproductive adults winged Populations as a whole are outbred One particular subterranean species, Reticulitermes flavipes, has poor dispersal abilities because of reduced wings Higher inbreeding depression (DeHeer and Vargo 2006)

18 Invertebrate Example: Social Spiders Multi-female groups, Diplo-diploidy Sociality in spiders has evolved several times Spiders in genus Anelosimus range from solitary to living in colonies >10,000 Only social species are inbred - WHY? Photo cr. Alex Wild

19 Social vs. Subsocial Anelosimus SOCIAL Larger, less abundant prey Few, large nests High parasite loads Predators abundant Intense rains that damage nests SUBSOCIAL Smaller, more abundant prey Many scattered, small nests Lower parasite loads Predators less abundant Less damaging environment

20 Social Subsocial

21 Conclusions Inbreeding has evolved in a wide variety of social taxa Can help to keep colony numbers high Often comes at a cost Mathematical models can predict when members of a species may choose inbreeding