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Alternative Reproductive Strategies

Alternative Reproductive Strategies. Not all individuals, particularly males, use the same strategy for courting females or otherwise gaining access to females. . Making the best of a bad situation - developmental basis, e.g., young males have noncourting strategies

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Alternative Reproductive Strategies

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  1. Alternative Reproductive Strategies Not all individuals, particularly males, use the same strategy for courting females or otherwise gaining access to females. • Making the best of a bad situation • - developmental basis, e.g., young males have noncourting strategies • until they achieve a larger size • - Dealt a poor hand for whatever reason (genes and/or env.) and they lack • the strength, fortitude, attractiveness, or charm to compete successfully • (2) Alternative strategies in evolutionary equilibrium (or non-EQ)

  2. Long horns for their BS There is a threshold body size for the morphological switch between horned and hornless. That it has a genetic basis was confirmed by Douglas Emlen in a 7 generation artificial selection experiment Short horns for their BS

  3. Fighter Sneaker Fighter 5 X 8 > Y Sneaker 7 > X 3 Y Recall that an evolutionary game can result in a mixed-strategy ESS: If S in a world of F > FF and F in a world of S > SS, then neither strategy alone can be the ESS. Instead we expect a mixture of S and F strategies such that each has equal fitness (e.g., reproductive success)

  4. In Coho salmon, proximity to the nest and the female during egg-laying influences the chances of fertilizing young. And there are 2 ways of getting close: Sneaking and Fighting Mixed ESS: being small is good for sneakers, being large good for aggression, and intermediate sizes are good for nothing

  5. Hooknose 1 2 3 Jack Female 1 2 3 • Hooknose • matures at 3 yrs - large • 2° sex characters: exaggerated snout, • enlarged teeth • Territorial, aggressive; fight for access • to females and winners mate These alternative strategies are played out by alternative male phenotypes.... • Jack • matures at 2 yrs - small • No 2° sex characters: cryptic • Non-territorial, gains access to females • by sneaking behavior to gain close • proximity to the nest

  6. Frequency Dependence? In a world of Hooknoses, fights are again rampant and individuals that sneak to gain proximity are favored  Jack is favored In a world of Jacks, competition intense, Jacks fight repeatedly, larger males win more fights  Hooknose is favored Fitness = (Repro.success) × (Prob. survival) Hypothetical relationship and as far as I know, untested. However, if the solution to this game is a multi-strategy ESS, then we predict the 2 strategies will have equal fitness....

  7. Jack success Hooknoses success 0.13 0.06 8.4 12.7 0.66 1 = 0.95 X X Hooknose Survivorship = 6% (2 yrs in ocean vs 1) Days reproductively active = 12.7 (greater stamina) Mean proximity to female = 93.0 cm Jack Survivorship = 13% Days reproductively active = 8.4 Mean proximity to female = 124.6 cm Assumption I: The number of mating opportunities is proportional to the number of days active on the breeding ground Assumption II: Relative proximity provides a relative measure of fertilization success for males – thus Jack success is 66% that of Hooknoses

  8. Rock-Paper-Scissors Game

  9. Scissors Rock Paper 0 -1 1 Rock 0 1 -1 Paper 0 Scissors -1 1 An Evolutionary Game with 3 males reproductive strategies In the Rock-Paper-Scissors Game each strategy is capable of beating one alternative strategy and each loses to one alternative strategy The result is a stable mix of 3 strategies, one can either: (1) Play R, P, and S with equal probability, i.e., 0.333. (2) Individuals play only R, P, or S, but their frequency is equal at 0.333.

  10. Orange-throated lizards – Ultra-dominant territorial males that attack other lizards and impinge on their territory seeking mates Yellow-throated lizards – Non-territorial, non-fighting, either flee or mimic a female’s (also yellow-throated) “not ready for copulation” display Blue-throated lizards – Territorial, but lower stamina and thus susceptible to territorial invasion A Rock-Paper-Scissors Game in the side-blotched lizard

  11. Fooled by Yellow’s female mimic displays and b/c they have reduced mate guarding (they’re off beating up the Blues) lose copulations to Yellows  Yellow beats Orange Intense mate guarding allows no opportunities for Yellows  Blue beats Yellow Orange – impinge on Blue territories and “steal” copulations  Orange beats Blue

  12. Blue invades a Yellow world Orange invades a Blue world Yellow invades an Orange world

  13. Populations of the 3 strategies cycle over time since no SINGLE strategy can persist as an ESS…..

  14. Sex-change as an Adaptation Initial phase (IP – females or males) Terminal phase (TP) – males only

  15. male Fecundity female age of size We’d expect sex change to occur whenever individuals would benefit (i.e., higher fitness) by changing The Size Advantage Model: ** In the above example we have ProtogynousHermaphrodites – sequential female to male strategy. Some fish are also Protandrous Hermaphrodites – sequential male to female strategy, but it is much rarer, e.g., clown fish Burning bridges -- No species changes sex multiple times

  16. Furthermore, these represent alternative male reproductive strategies (sneaking and territorial males) as we’ve just discussed. Its rare to have both sex change and alternative male phenotypes in the same spp. Bluehead Wrasse Polymorphism between ProtogynousHermaphrodites and non-sex-changing males female floater IP male territorial TP male male

  17. Robert Warner’s work on the Bluehead Wrasse has shown: (1) Size matter: TP males have 25x the mating opportunities per day as females  So sex change is in the correct direction (2) When to change? The Size Advantage Model predicts reproductive success of males exceeds females at 75mm in length  This matches the average size of sex change (3) Furthermore, sex change is socially controlled: Females are keenly sensitive of their the immediate prospects as male or female and i) The largest female will initiate sex change almost immediately upon removal of the locally dominant TP male ii) Within minutes will behave as a male and court and mate with females the DAY of sex change iii) Is capable of producing sperm in as few as 5 days after initiation of sex change

  18. Why sex change in the Bluehead Wrasse? • Marine reef fish – In general, recruitment of young to reefs is extremely • sporadic and episodic. So demography (age breakdown of the population) is • unpredictable • given the timing and magnitude of arrival, an individual of a particular size may be either relatively small or large – greatly affecting its chances of successfully attaining territorial male status • Caribbean fish – Its always good to reproduce • females = 480 times in first 2 yrs and if they survive to a TP males, another 2300 times • when organisms mate so frequently, each mating opportunity has little value, instead, emphasis is given to staying alive as long as possible. Thus female pick SAFE mating sites which they are extremely faithful to. The consequence of this is that there is extreme male-male competition for territorial status and defense of those sites

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