Some misconceptions promulgated Discovery series: “Life” (3/ ) 1. female poison frog: “has to get tadpoles to safety.” 2. female octopus: “blows water over her eggs to help them breath.” 3. “amphibians have no scales, no claws, so they have had to evolve different (survival) strategies. 4. female chameleon in Namib Desert: moving across the dunes “looking for love.” 5. male African bullfrog: “tadpoles will begin to suffocate within one hour unless he can do something about it.” 6. Sea krait: “needs to make sure eggs are safe.” “found a solution.”

Life histories and reproductive mode Two principles: 1. Small genetic component in life history variation. – Flexibility is important 2. Life history characteristics have not evolved in order to perpetuate a species. – Shaped by natural selection increasing fitness of individuals.

Life histories and reproductive maturity E.g., insects

Reproductive effort—Index of the proportion of biomass allocated to inflorescences—in annual (semelparous) and perennial (iteroparous) species of British grasses Semalparity in males of Antechinus sps.

Trade-off between number of seeds and their size among Goldenrods (Solidago)

Trade-off between age of reproductive maturity and adult mortality rate

Guppies: selection for age at reproductive maturity ♀♂

Selection for size of female (first birth) and size of offspring ♀

Sex and Reproductive Success Sex as an Adaptation Since most species are bisexual (gonochoristic), there must be some advantage to sexual reproduction. Resistance against parasites? Sexual reproduction promotes genetic recombination Trade-off: separating favorable gene combinations. If A1 is always associated with B1 and A2 with B2, the genes are in linkage disequilibrium. Linkage equilibrium is achieved by crossing over. Eventual result = association of 2 or more alleles at the frequency predicted by their individual frequencies.

Bringing together A 1 B 1 / A 1 B 1 and A 2 B 2 / A 2 B 2 in the same population A 1 B 1 / A 2 B 2 Decay of linkage disequilibrium Continues until alleles at The 2 loci are randomly associated with each other A and B are in linkage equilibrium if (gAB*gab) – (gAb*gaB) = 0

Countering linkage equilibrium: Primulus vulgaris Heterostylous G and A closely linked 1. Keep genes together that promote outcrossing

2. Reproduce asexually e.g., unisexual vertebrates Shared features 1. Originate by hybridization 2. Exclusively female 3. There is an aberrant gametogenic mechanism – mitotic or meiotic 4. Genetic recombination is usually absent so that inheritance is clonal. 5. Polyploidy can occur if synapsis between non- homologous chromosomes does not have to occur or if homologous chromosomes can be produced.

Four Reproductive Modes

An hypothesis (Maynard Smith): Asexual reproduction (all females) should be twice as advantageous as sexual reproduction--where half of the population are males. Theoretical basis – Female fitness is maximized if her genes are not “wasted” in the production of males.

However, when actual asexual populations are studied e.g., (parthenogenetic vertebrates) there are some obvious disadvantages. 1. An asexual mechanism in vertebrates is difficult to produce. 2. The two sexual species that hybridize to produce successful asexual entities: – A. must be sufficiently divergent genetically to modify normal meiosis but – B. can’t be too divergent genetically or development will be abnormal. a proportion of parthenogens hatched in the lab have developmental deformities