7 Other alternative tactics While dominant gray seal males fight over access to females that are hauled out on beaches with their pups, sub-dominant males look for and find mates swimming out in the water near the colonyIt takes 3 minutes for a male marine iguana to ejaculate and small males are forcibly removed from females.To cope, small males ejaculate prior to mating and store their sperm in their bodies, then evert their penis when mating with their partner.
8 Conditional Mating Strategies Or…making the best of a bad situationGoing to be scrawny and uncompetitive with the large males?No problem, grow big testes!
14 Sperm CompetitionCompetition among males to fertilize females doesn’t stop at ejaculation1st male advantage – often seen in external fertilizing species, as well as species with sperm storage capabilitiesLast male advantage – Common in species that can remove competing sperm
15 Sperm competitionSelection can act on sperm morphology, sperm number, as well as females’ ability to control fertilization successDrosophila bifurca have 58mm long sperm!Wood mice sperm have an apical hook used to attach to other sperm and create mobile trains, which have higher fertilization success than individual spermA splendid fairy wren male may have 8 billion sperm at any given time
16 Across taxonomic groups, in species that have a high potential for sperm competition, there are relationships between sperm competition and ejaculate quality/sperm production
17 In birds, there is a direct relationship between levels of extra-pair paternity and testis mass
18 Sperm Competition Selection on sperm can also occur within a species Older, territorial males nesting in the interior of a colony produce ejaculates with more sperm that swim faster, giving them a fertilization advantageSneakers may release their sperm at exactly the same time, but sneakers will fertilize more eggsSperm competition occurs across the animal kingdom
19 Removing competing sperm Male black-winged damselflies use a spiky, modified penis to scrub out and remove gametes from the female’s sperm storage organ before transferring their own sperm.Male dunnocks peck at the cloaca of their partners if they find another male near her. This behaviour results in her ejecting a droplet of ejaculate from the other male.
20 Copulatory plugsObserved in mammals, spiders, reptiles, and insects, copulatory plugs are inserted just after copulation in order to limit subsequent copulations by another male.The golden orb spider, Nephila fenestra males take this to a whole new level
22 Females still hold the cards Females may store the sperm of their social partner, but instead use recently received sperm from an extra-pair partner to fertilize the egg.
23 Tree swallows are socially monogamous migratory passerines Both males and females provide parental care to offspringHave one of the highest rates of extra-pair paternity in any bird species (83% of nests, 47% of nestlings in an Ontario Population; Stapelton et al. 2007)Thus, selection will act strongly on males to assure fertilization success.
29 Female Defense Polygyny Theory: When receptive females cluster, males may compete directly for those clusters, resulting in female defense polygynyEvidence: Monogamy (in mammals) never occurs when females live in groupsIn many groups, females congregate for protection against predators and males compete to control sexual access to the group.
30 Montezuma oropendolas monopolize females in small colonies, but once the colony gets large, it becomes difficult to defend and maintain
31 How do we know it’s actually female defense? Couldn’t it just be territory defense?
32 Marine siphonoecetine amphipods construct elaborate homes Marine siphonoecetine amphipods construct elaborate homes. When males encounter a female, they glue her home to their own, creating an apartment complex
33 Resource Defense Polygyny This African cichlid, Lamprologus callipterus, creates a shell midden that he defends against predators and other males. Females bring their eggs to the midden and nest within one of the shells. Up to 14 females may nest within the male’s large midden
34 Changes in the distribution of resources can change the mating system of dunnocks