Evolution and Life Histories II

LH example: Thrip egg mites LS: 4 days

Life History Principles Generally begin with birds Reproductive output is accessible. Reproductive output can be easily manipulated and adjusted. Individuals can be marked for identification.

The evolution of clutch size Optimal clutch size ? How much energy should an individual allocate to an episode of reproduction; e.g., how many eggs? Trade-off: The more offspring produced, the fewer resources available for each individual. Lack’s prediction: Selection should favor a clutch size that maximizes the number of surviving offspring. Clutch size should be a reproductive strategy.

Tradeoff: Probability of individual survival clutch size Prediction: Number of surviving offspring = clutch size x probability of individual survival Optimal clutch size = 5 Assumptions: 1. eggs are all the same size 2. current reproductive effort does not affect subsequent performance Starting hypotheses

A test of the prediction: Number of Clutches N = 4489 Number surviving as a function of clutch size Parental lifetime fitness can decrease from care necessitated by large broods.

Future effects of clutch size on daughters’ performance Collared Flycatchers

Effect of age at first reproduction on size of subsequent clutches e.g. Collared Flycatchers Begin at different ages Begin with extra eggs

How large should offspring be? Trade-off between number and size of offspring. Produce many small OR few large? Can be dictated by environmental context; i.e., the reproductive strategy may include phenotypic plasticity e.g. Stator limbatus (a seed beetle)

Seed beetle: Stator limbatus Blue palo verde seed Poor host: < 1/2 larvae survive Cat-claw acacia seed Good host: most larvae survive

Optimal offspring size for parent is larger on poor host Minimum size at which offspring survive is smaller on good host The model: Size decreases with an increased number of sibs Offspring survival Parental fitness Prediction: larger eggs on poorer host Stator limbatus

1st egg on on host - then switched Restricted to one host

A phylogenetic constraint on clutch size. A fitness enigma?

A. tesselata (24.2 mL) A. neotesselata (17.0 mL) A. sexlineata (7.1 mL)

Karyotype of Aspidoscelis neotesselata

Intraspecific divergence in life histories in A. tesselata (a parthenogenetic species)

Fort Sumner

Aspidoscelis tesselata Pattern class EPattern class C

Assignment: Sunday March 21 Watch “Life”: Cable TV, Discovery Channel Making the series, 6 P.M. Reptiles and Amphibians, 7 P.M.