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 colony It 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.
Conditional Mating Strategies Or…making the best of a bad situation Going to be scrawny and uncompetitive with the large males? No problem, grow big testes!
Sperm Competition Competition among males to fertilize females doesnt stop at ejaculation 1 st male advantage – often seen in external fertilizing species, as well as species with sperm storage capabilities Last male advantage – Common in species that can remove competing sperm
Sperm competition Selection can act on sperm morphology, sperm number, as well as females ability to control fertilization success Drosophila 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 sperm A splendid fairy wren male may have 8 billion sperm at any given time
Across taxonomic groups, in species that have a high potential for sperm competition, there are relationships between sperm competition and ejaculate quality/sperm production
In birds, there is a direct relationship between levels of extra-pair paternity and testis mass
Sperm Competition Older, territorial males nesting in the interior of a colony produce ejaculates with more sperm that swim faster, giving them a fertilization advantage Sneakers may release their sperm at exactly the same time, but sneakers will fertilize more eggs Sperm competition occurs across the animal kingdom Selection on sperm can also occur within a species
Removing competing sperm Male black-winged damselflies use a spiky, modified penis to scrub out and remove gametes from the females 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.
Copulatory plugs Observed 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
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.
Tree swallows are socially monogamous migratory passerines Both males and females provide parental care to offspring Have 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.
Female Defense Polygyny Theory: When receptive females cluster, males may compete directly for those clusters, resulting in female defense polygyny Evidence: Monogamy (in mammals) never occurs when females live in groups In many groups, females congregate for protection against predators and males compete to control sexual access to the group.
Montezuma oropendolas monopolize females in small colonies, but once the colony gets large, it becomes difficult to defend and maintain
How do we know its actually female defense? Couldnt it just be territory defense?
Marine siphonoecetine amphipods construct elaborate homes. When males encounter a female, they glue her home to their own, creating an apartment complex
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 males large midden
Changes in the distribution of resources can change the mating system of dunnocks