| Dept of Biology, Lewis and Clark College | Dr Kenneth Clifton
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Biology
352 Lecture Outline
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Mating System Evolution
Mating systems encompass the collective behavioral and morphological traits associated with interactions between the sexes for the purposes of sexual reproduction.
Given that reproduction represents a critical feature of overall fitness, there is often strong selection for traits that provide even small advantages over competition for resources (females) or mates (males).
For each sex, consider how fitness is potentially influenced by various factors...
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| Encounter rate |
with females (e.g. insects waiting near emergence sites, elephant seals at haul out beaches) |
with males (e.g., use pheromones or other signals, visit many males, etc.) |
| Fraction of encounters that have potential for fertilization |
females that are inseminated (e.g., Bruce effect, forced insemination) |
Number of eggs ready for fertilization (increase access to resources via territoriality, dominance |
| Fraction of eggs fertilized |
Number of eggs fertilized per inseminated female (e.g., female guarding, mating order, reaming, dilution, sperm plugs) |
Fraction of eggs fertilized (e.g., sperm limitation.... reduce encounters with other females, mate multiple times). |
| Survival from zygote to adulthood |
(e.g., nuptial gifts, large spermatophores, female provisioning, egg guarding, nestling feeding, etc.) |
(maternal care, select male with territory, food provisioning, or parental care) |
| Adult life expectency |
male life expectancy (defer breeding, reduce risky strategies, defend territory |
Adult female life expectancy |
| Nepotism correction |
(increase fitness by favoring kin) |
(increase fitness by favoring kin) |
| Sexual selection correction |
(increase fitness by mating with females that prefer certain male traits) |
(increase fitness by mating with males with certain traits) |
| Demographic correction |
(increase fitness by breeding earlier or later than others in the population.... uncommon) |
(increase fitness by breeding earlier or later than others in the population) |
Numerous different behavioral strategies (5-10) may evolve to improve each of these components.Not surprisingly, an enormous number of behavioral combinations are possible.
Which combinations are ultimately selected depends on:
Environmental constraintsResource availability, disturbance, temperature, etc..... an optimality problemIntrasexual interactions
The optimal strategy within a sex depends upon what other members of the same sex are doing... Male/male competition may be especially importantIntersexual interactions
The optimal strategy for one sex may depend upon the strategy adopted by the opposite sex.... This can lead to patterns of parental care, mate searching strategies, female choice, etc...
Specific mating systems evolve because certain combinations of these three variables influence individual fitness in ways that produce ESS conditions.
Despite the myriad possibilities, some basic patterns emerge
Basic categorizations of matings systems are:
Monogamy: one male with one female, extended pair bond, often shared parental carePolygyny: one male with several females, often with extended pair bonds, usually female parental care or no care
Resource defense vs. female defense... models to polygyny threshold
Polyandry: one female with several males, often with extended pair bonds, usually male parental care
Polygynandry: females mate sequentially with several males, males mate simultaneously with several females, short-lived pair bonds, usually male parental care
Promiscuity: both sexes may have multiple mates, no pair bonds and either female or no parental care.
The evolution of these different mating strategies depends on patterns of resource availability, predation risk, environmental stability, and levels of parental care.
Careful...The same basic pattern of mating behavior may evolve for several different reasons.The components used to describe the system are not necessarily the causal factors.
Most male strategies are geared towards improving female encounter rates and fertilization rates.
Most female strategies are geared towards improving access to resource and ensuring offspring survival.