III Sex and Selection A Costs and Benefits

III. Sex and Selection A. Costs and Benefits 1. Asexual - major benefit of asexual: maximizes transfer of genes to next generation, and maximizes survivorship in a constant environment “Vegetative” Reproduction: Growth and fragmentation

Vegetative reproduction in animals

Parthenogenesis: Production of gametes that develop without fertilization Aphid ‘stem mother’ producing offspring parthenogenically May be as high as 22% in Copperheads. Cnemidophorus nemexicanus in middle, flanked by diploid parent species. Bees and wasps – males are haploid offspring Rare but observed in zoo populations of Komodo dragons. Mulga (Australian Acacia)

Parthenogenesis: Production of gametes that develop without fertilization A B a b Direct development from oogonium to egg, and subsequent mitotic divisions to produce embryo – GENETICALLY IDENTICAL TO MOTHER AABB AB A B a b AAbb Ab Meiosis I a. B ab Separation of chromatids without cytokinesis results in diploid eggs that are not identical to mother or each other aa. BB aabb

III. Sex and Selection A. Costs and Benefits 1. Asexual - major benefit of asexual: maximizes transfer of genes to next generation, and maximizes survivorship in a constant environment - major costs of asexual: “all or none” survivorship in changing environment, and “Muller’s Ratchet” Mutations can only accumulate in a lineage; all genes passed to all offspring.

III. Sex and Selection A. Costs and Benefits 1. Asexual - major benefit of asexual: maximizes transfer of genes to next generation, and maximizes survivorship in a constant environment - major costs of asexual: “all or none” survivorship in changing environment, and “Muller’s Ratchet” 2. Sexual: - major cost: only ½ genes to each offspring (not necessarily complementary sets, either. Only 1 in ~8 million chance of producing two gametes that have receive opposite homologs from each homologous set in humans).

III. Sex and Selection A. Costs and Benefits 1. Asexual - major benefit of asexual: maximizes transfer of genes to next generation, and maximizes survivorship in a constant environment - major costs of asexual: “all or none” survivorship in changing environment, and “Muller’s Ratchet” 2. Sexual: - major cost: only ½ genes to each offspring - major benefit: extraordinary production of variation; sexual lineages are more likely to survive over time in changing environments, and adapt to rapidly evolving parasites.

The “Red Queen” Hypothesis Parasites have shorter life spans than their host, and so have more opportunities for selection to adapt them to their hosts. Host must continually ‘reshuffle the genetic deck” to stay ahead of their parasites…

Moran et al. , (2011) Running with the Red Queen…. Science 333: 216 -218. Experiment 1: rates of sexual reproduction in wild-type populations of C. elegans C. Elegans are either males or hermaphroditic females that can reproduce by self fertilization (not parthenogenesis). They are parasitized by bacteria, that can kill them in 24 hrs. In the absence of parasites, selfing-fertilization is preferred (80%: 20%). Repeated exposure to the same strain of parasite selects for outcrossing (80%), until an adapted genotype is produced that is resistant. Then reproduction ‘relaxes’ to selfing. Wildtype outcrossing rates over time. Outcrossing rates in wildtype populations were not manipulated and free to evolve during the experiment. The wildtype populations were exposed to three different treatments: control (no S. marcescens; dotted line), evolution (fixed strain of S. marcescens; dashed line), and coevolution (coevolving S. marcescens; solid line) for thirty generations. Error bars represent two standard errors of the mean (SE). Continued exposure to an evolving parasitic population selects for increasing rates of outcrossing reproduction.

Females can reproduce parthenogenically or sexually. As parasitism rates by a trematode parasite increase, so does the abundance of males (and sexual reproduction) in the population.

III. Sex and Selection A. Costs and Benefits B. Sexual Selection - results when there are unequal investments in offspring/reproduction. 1. Investment in Gametes and Offspring - many small sperm: maximize number of matings and offspring (component of fitness #2) - a few large eggs: maximize quality of offspring. (componentof fitness #3)

Kiwi: Large Egg = 25% of body weight Make it count! Nesting, parental care

- many small sperm: maximize number of matings and offspring (component of fitness #2) Parental care may not be adaptive, unless both parents needed to raise offspring. Better to spend time mating again.

III. Sex and Selection A. Costs and Benefits B. Sexual Selection - results when there are unequal investments in offspring/reproduction. 1. Investment in Gametes and Offspring 2. Investment in mating: monogamy vs. polygamy The sex that invests more energy in reproduction should be choosy (monogamous) Also, the sex with lower reproductive potential (lower maximum fecundity) should be choosier. NEWTS # offspring male Jones (2002) female # mates

III. Sex and Selection A. Costs and Benefits B. Sexual Selection - results when there are unequal investments in offspring/reproduction. 1. Investment in Gametes and Offspring 2. Investment in mating: monogamy vs. polygamy Also, the sex with lower reproductive potential (lower maximum fecundity) should be choosier. PIPEFISH # offspring female Jones (2002) male # mates

III. Sex and Selection A. Costs and Benefits B. Sexual Selection - results when there are unequal investments in offspring/reproduction. 1. Investment in Gametes and Offspring 2. Investment in mating: monogamy vs. polygamy 3. Intrasexual selection: competition within a sex for access to mates Which sex will experience sexual selection? The one with greater variance in reproductive success.

Sexual Selection 3. INTRAsexual Competition - competition for harems, territories

Male mortality is high when battling for a harem, and reproduction is high only for males during harem dominance.

Sexual Selection 3. INTRAsexual Competition - competition for harems, territories - sperm competition

Sexual Selection 3. INTRAsexual Competition - competition for harems, territories - sperm competition - infanticide

Sexual Selection 3. INTRAsexual Competition - competition for harems, territories - sperm competition - infanticide - female mimicry in male subadults and "stealth matings"

"sneaker males" FEMALE "Sneaker" male

Sexual Selection 3. INTERsexual Selection (Mate Preference) - A behavior or morphology that is only performed during the reproductive season, which DECREASES SURVIVORSHIP. Only adaptive because it INCREASES THE PROBABILITY OF REPRODUCTION disproportionally.

Sexual Selection 3. INTERsexual Selection (Mate Preference) - A behavior or morphology that is only performed during the reproductive season, which DECREASES SURVIVORSHIP. Only adaptive because it INCREASES THE PROBABILITY OF REPRODUCTION disproportionally. showy breeding plumage calling displays

3. INTERsexual Selection (Mate Preference) - WHY is it ADAPTIVE for the FEMALE to choose a given male? ? 1. Direct Benefit - nuptual gifts (energy for egg making) Dance flies Scorpionflies

3. INTERsexual Selection (Mate Preference) - WHY is it ADAPTIVE for the FEMALE to choose a given male? ? 1. Direct Benefit - nuptual gifts (energy for egg making)

3. INTERsexual Selection (Mate Preference) - WHY is it ADAPTIVE for the FEMALE to choose a given male? ? 1. Direct Benefit - high resource territories The polygamy threshold: If resources are limiting and patchy, a resident on a high quality territory may provide more resources to TWO mates than a resident on a low quality territory could provide to ONE mate. Selection may favor polygamy (unless both parents are needed to raise offspring).

3. INTERsexual Selection (Mate Preference) - WHY is it ADAPTIVE for the FEMALE to choose a given male? ? 1. Direct Benefit - parental care

3. INTERsexual Selection (Mate Preference) - WHY is it ADAPTIVE for the FEMALE to choose a given male? ? 1. Direct Benefit 2. Indirect Benefit: Good Genes - ‘Handicap Theory’

3. INTERsexual Selection (Mate Preference) - WHY is it ADAPTIVE for the FEMALE to choose a given male? ? 1. Direct Benefit 2. Indirect Benefit: Good Genes - handicap theory and runaway selection

3. INTERsexual Selection (Mate Preference) - WHY is it ADAPTIVE for the FEMALE to choose a given male? ? 1. Direct Benefit 2. Indirect Benefit: Good Genes - ‘Parasite Load Theory’

3. INTERsexual Selection (Mate Preference) - WHY is it ADAPTIVE for the FEMALE to choose a given male? ? 1. Direct Benefit 2. Indirect Benefit: Good Genes - ‘Symmetry Theory’ Hmmm. . Some studies show a preference for mates that are more symmetrical. Post-hoc explanations suggest this might be adaptive because symmetry arises as a consequence of integrated development on both sides of the body, perhaps as a consequence of a well-integrated genome.

3. INTERsexual Selection (Mate Preference) - WHY is it ADAPTIVE for the FEMALE to choose a given male? ? 1. Direct Benefit 2. Indirect Benefit: Good Genes - ‘Symmetry Theory’ Hmmm. .

3. INTERsexual Selection (Mate Preference) - WHY is it ADAPTIVE for the FEMALE to choose a given male? ? 1. Direct Benefit 2. Indirect Benefit: Good Genes - ‘Symmetry theory’ Hmmm. .

3. INTERsexual Selection (Mate Preference) - WHY is it ADAPTIVE for the FEMALE to choose a given male? ? 1. Direct Benefit 2. Indirect Benefit: Good Genes - ‘Symmetry Theory’ Hmmm. . Hey, It Works!!

III. Sex and Selection A. Costs and Benefits B. Sexual Selection - results when there are unequal investments in offspring/reproduction. 1. Investment in Gametes and Offspring 2. Investment in mating: monogamy vs. polygamy 3. Intrasexual selection: competition within a sex for access to mates 4. Sexual conflict: male and female strategies may be at odds - males are competing with other males. Traits that reduce female survivorship after mating, fertilization, and egg laying increase the male’s fitness over other males. - selects for counter-measures in females to increase her lifespan, and increase her mating probability to choose the best mate.

III. Sex and Selection A. Costs and Benefits B. Sexual Selection - results when there are unequal investments in offspring/reproduction. 1. Investment in Gametes and Offspring 2. Investment in mating: monogamy vs. polygamy 3. Intrasexual selection: competition within a sex for access to mates 4. Sexual conflict: male and female strategies may be at odds Investment in testis and sperm can be high if there is sperm competition. (Drosophila bifurca).

Male Drosophila produce a toxin that kills female. But when forced to mate monogamously for 30 generations, there was selection for reduced toxin levels and reduced toxin defenses. When these females were exposed again to wildtype males with normal high levels of toxins, there was increased mortality.

During mating, females try to throw off males shortly after mating… decrease sperm load, increase her choice. Males have evolved structures to hang on more tighly, including odd, gripping antennae. The gen distalless (dll) controls growth of extensions. When down-regulated, lower reproductive success.