Reproductive Tactics


Costs of reproduction
Tradeoffs between present progeny and expectation of future progeny.
Reproductive effort, relative clutch mass (RCM)
Residual reproductive value
Expenditure per progeny (EPP), neonate size
Triumvirate: Clutch size = RCM/EPP

Age of onset of sexual maturity, single brood vs. multiple clutches
r selection verus K selection (r-K selection continuum)
Bet hedging (unpredictable variable juvenile mortality)
External versus internal fertilization (certainty of paternity)
Parental care

Lizards and Snakes

Sperm storage, parthenogenesis
Gonadal activity & mating behavior can be associated or dissociated
Widely foraging species with large body sizes and small clutches at one end of an axis, and sit-and-wait foragers with small body sizes and large clutches at other end of spectrum (Dunham and Miles 1985)
Viviparity has evolved multiple times among squamates via egg retention, primarily in colder climates (high latitudes and altitudes)

External fertilization, amplexus, high fecundity, high larval mortality
Trend towards increasing terrestriality
Male paternal care, egg brooding, pouches, gastric brooding, etc.

Spermatophores (internal fertilization), low fecundity, trend towards increasing terrestriality, viviparity has evolved

Internal fertilization, high survivorship, low fecundity, parental care, viviparity

Conservative, no parental care, large clutches, high juvenile mortality
Terrestrial tortoises have invest relatively more per progeny

Large clutch size, female guard nests and young

Sexual Selection, Sexual Dimorphism
Males often larger than females, sometimes with proportionately larger heads
In territorial lizard species, males larger, defend a "harem" of females
Recent study showed that sexual size dimorphism correlates with female density in Anolis even after phylogenetic effects are removed via Felsenstein independent contrasts (Stamps, Losos, and Andrews 1997)

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Last updated 20 Feb 1997 by Eric Pianka