Transcript CH12L2
Extra pair copulation vs. polyandry/polygamy EPC = copulations that occur outside an identifiable reproductive pair •The pair must be sharing “non-copulatory’” reproductive efforts •Even if disproportional •The extra pair copulation must be “against the will and wishes” of the partner. •i.e. “cheating” •Should not result in diversion of significant parental resources from cheater Polyandry and polygamy on the other hand •Can occur even in the presence of a pair bond relationship •Would not be disputed by the partner •Can cost the other partner in terms of fitness (short-term or overall) •Typically results in division of parental resources Extra pair copulations (EPC) EPC advantages Males: •More offspring •Mix genes with a greater variety of females •Increased fecundity (reproductive capacity) Females: •Access to better genes •Increased probability of fertility •Increased gene compatibility Partner disadvantages Males: •Wasted parental effort •Decreased fecundity Females: •Potential loss of paternal effort •Potential loss of paternally controlled resources Polygyny advantages: Males: •Access to more females •Mix genes with a greater variety of females •Increased fecundity Females: •Access to dominant males (good genes) •If females are related they can share.. •territory defense responsibility •offspring defense responsibility Partner disadvantages: Males must typically defend: •Reproductive rights •Territory/resources •Failure can lead to infanticidal acts against his offspring Females typically loose: •Reproductive “freedom of choice” •Decreased paternal effort as a function of harem size. •Change in dominant male can lead to loss of offspring •Lowering overall fecundity Polyandry generally speaking is rare and usually occurs when females or resources are in extremely short supply Polyandry advantages: Males Some access to females (you don’t play you cant win) Submission to this strategy = increased fecundity Shared defense of offspring Shared defense of resources Females Access to more males Mix genes with a greater variety of males Increased fecundity Partner disadvantages Males No or low mate selection opportunity Paternal uncertainty Wasted paternal effort Females May have to assume roles typical of males such as Harem defense Offspring defense A final note on polygyny polyandry and monogamy There are many varieties of these basic mating systems identified some of which are described in the book. The name of each system is based on the hypothetical key factor that is believed to have been the evolutionary force behind the evolution of that specific system. For example: Lek polygamy •Males collect in a very restricted physical space •Lek position/formation does appears to correlate to density of females/ nesting areas •Lek position tends to be relatively stable annually •This position is poorly corrleated to resources •Typically males of these species are ornately decorated •Males will perform ritualistic displays •Dances •Plumage displays •Ritualistic fights •Females enter the lek, observe, then select a mate •Typically a relatively few males are reproductively successful •Males typically provide resources or parental effort Prairie Chicken Lordotus bee fly Sage Grouse Fallow deer: population density-dependent lek polygyny Fallow deer exhibit typical polygynous behavior: •dominant male holds/defends and reproduces with a harem Under conditions of high population density: Males move to common rut place (October) •Each male defends and marks a small stand within place •Females approach rut place. •Dominant males in middle copulate. •May start with lekking followed by harem holding •only 10% males in a lek will mate The bee fly Lordotus pulchrissimus Arial leks •Are in the same place daily and annually •Position cue have not been discovered •No apparent correlation to shrub position •No evidence of pheromone cues 9 lek sites in a 400 m by 700 m have persisted for 5 years