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Some more unusual reproductive strategies. 2. Sexual cannibalism 3. Male as sperm bank 4. Hermaphrodites 5. Alternative strategies. Some more unusual reproductive strategies. 2. Sexual cannibalism 3. Male as sperm bank 4. Hermaphrodites 5. Alternative strategies.
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Some more unusual reproductive strategies 2. Sexual cannibalism 3. Male as sperm bank 4. Hermaphrodites 5. Alternative strategies
Some more unusual reproductive strategies 2. Sexual cannibalism 3. Male as sperm bank 4. Hermaphrodites 5. Alternative strategies
Copulation begins with the male standing on the female's abdomen, 'belly to belly'. The male has two copulatory organs (palps) that are attached at the front part of his 'head'. Copulation begins when one of the palps is inserted into the female's genital opening. In most other black widow spiders, the pair copulates while in this posture. • (B) In redbacks, however, a few seconds after palp insertion, the male, using the palp as a pivot, moves into a 'headstand' posture. (C) The male then quickly turns through 180 degrees, landing with his 'back' directly above the female's fangs. In most matings, the female begins to extrude digestive enzymes almost immediately. She also pierces the male's abdomen with her fangs and begins to consume him while he is transferring sperm. http://www.scar.utoronto.ca/~mandrade/index.html
Sexual cannibalism – Why? • She’s hungry! • She gets the best male this way: • duds get eaten before they can mate • He provisions his future offspring • He functions as a ‘sperm plug’ • Maydianne Andrade study: • Males that are cannibalized mate more than twice as long as non-cannibalized males. They also father twice as many offspring with a female that mates with other males (sperm competition). • Cannibalism provides males extra time to put a plug in a female’s sperm receptacle. The plug prevents other males from fertilizing the female, thus raising the odds that the first male’s sperm will. • Male redback spider has two sexual organs, and females have two receptacles, each of which must be fertilized by separate male organs. If a male redback dies before he has a chance to fertilize the second receptacle, his reproductive success drops by half.
Hermaphroditic Species Many sea slugs are hermaphrodites
Hermaphroditic Species Suppose you could be male orfemale... • Many species of fish are hermaphrodites: • At least fourteen families of fish have females that may later switch to males • At least eight families have males that may later switch to females • In several species of fish, individuals are both male and female at once!
Fish Reproductive Strategies • Gonochorism: two distinct sexes • Hermaphroditism: individual has capacity to be male or female • Sequential • Protogynous (female to male) • Protandrous (male to female) • Simultaneous
an individual that changes sex at the right size or age will have more offspring than one that remains exclusively male or female Indeterminate Growth & Hermaphroditism in Fishes • Female fertility dependent on her size • Male fertility dependent on number of matings and partner’s fertility
Mating Systems in Sequential HermaphroditesSize Advantage Theory Large male dominates territory or harem →protogyny Random pairings →protandry ♀ ♂ ♂ ♀
Large male with female mate Group spawning Bluehead Wrasse a protogynyous (female to male) species Why different mating systems? • Large (Terminal Phase or TP) males are territorial • Small (Initial Phase or IP) males engage in group spawning and ‘sneaking’
Bluehead Wrasse a protogynyous (female to male) species Resource defense polygyny. Male defends nesting niches in coral reef. Typically has 3-6 females in his territory. Fights off other males.
Wrasse Removal Experiments Removal of male triggers sex change in largest female Change evident in 1.5 hours Male-style courtship begins in 2-4 days Sperm production in 14-18 days Presence of (large) male inhibits sex-change
♂ ♀ Guess who’s Protandrous?
Develop into males first and then potentially into females when older/larger Clownfish live in small groups, one group per anemone, composed of a breeding pair and 1-4 non-breeders. The group is dominated by the top- ranking female breeder, the largest fish. Her male partner is next in rank and size, followed by 1-4 progressively smaller and lower-ranking, non-breeding subordinates. Clown Fish (Anemone Fish) a protandrous (male to female) species
When the dominant breeder in a group dies, all the fish move up a social level. The top male changes sex to become the primary female, the top-ranking non-breeding subordinate becomes a sexually active male and all the other subordinates shift up a rank Clown Fish (Anemone Fish) a protandrous (male to female) species
Simultaneous Hermaphrodites • Which role should you take - male or female? • Solutions: • Mate 1x/day (dusk) • Parceling • Egg trading • = Tit for Tat? Hamlets
Bowerbirds: Sexual selection has produced bizarre structure-building behaviors and displays What is different about bower vs. morphological trait? (e.g., plumage)
catbirds related to bowerbirds but only construct cleared display courts Fig 10.4 Alcock Arbitrary? Or does bower-building ability tell you something about bird’s brain?
Like Bowerbirds, human ornamentation is arbitrary. Ideals of beauty vary greatly between cultures and times.
Bet-hedging hypothesis: multiple mating decreases variance in RS and hence increases the geometric mean fitness when there are mate choice and/or environmental uncertainties. A = arithmetic mean = (X1 + … + XN) / N G = geometric mean = (X1∙ … ∙ XN) 1/N G=A–2/2
Male as sperm bank • Deep-sea anglers • Males attach to females • Males parasitize female’s nutrients • Females gain control of male’s sex organs
Deep-sea anglerfish male is much smaller than the female, and lives as a permanent parasite on the female. The male attaches himself, by biting, to the body of the female. His mouth fuses with her skin, and the bloodstreams of the two fishes become connected. The male is now totally dependent on the female for nourishment. The male begins to degenerate. His eyes grow smaller and he eventually loses them. His internal organs disappear. The male becomes simply a source of sperm. Deep sea anglerfish
What are the possible reasons for a ‘monogamous’ female to mate with ‘extra-pair’ males? • Her social mate has below-average genetic quality • Her social mate is sterile • She wants additional help or resources for her kids • Her social mate has incompatible genes • She wants genetic diversity in her offspring • She wants to confuse everyone about who’s the father* *relates to multiple mating but not to the social monogamy + shared P.C. case
