BIO220H1 Lecture Notes - Lecture 14: New Zealand Mud Snail, Omphiscola Glabra, Trematoda
Lecture 14 reading
Mating Systems in Sexual Animals
Mating systems are important to understand because they reflect the
result of natural selection on mate choice, and ultimately on strategies
for maximizing individual reproductive success.
•males and females approach mating with different strategies
•When choosing mates, animals evolve species-typical strategies
for maximizing their reproductive success —> results in
considerable diversity among animal species in their mating
patterns.
The Evolution of Sex
sexual selection is more common than asexual because it has several advantages
•genetic recombination : gives genetic diversity
•increases the chances of acquiring favourable mutations and is unlikely to propagate
deleterious ones.
•advantageous as the local environment changes.
-e.g. Aphids—> in stable condition, asexual. in harsh env (cold weather), sexual (sexual
reproduction produces eggs that are freeze tolerant and can diapause during the winter)
-mud snail (Potamopyrgus antipodarum)—> Sexual individuals of this species are more
common in areas where risk of trematode infection is high. genetic diversity acquired
from sexual reproduction is necessary for this species to defend against parasites, as
asexual individuals may not easily survive in areas where parasites are high.
Sexual reproduction involves evolutionary differentiation of males and females:
•female : few gametes, invests more, male: invests less, many gametes
•Females may spend more care than males selecting a mate due to the high cost of their
gametes.
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Variance in Mating Success and Bateman's Principle
Bateman's principle: variance among females in mating success is low, whereas
variance among males in mating success is high.
-nearly all females in a population mate and have offspring, but relatively few males mate
successfully and those that do mate tend to mate with many females (thus a few males have
very high reproductive output, but many males have little or no reproductive output)
-sexual selection should act more strongly on males, leading to greater elaboration of
behaviour and structures used in attracting mates in males than in females.
controversies with Bateman’s theory: there are several advantages in female multiple mating
1) female cichlid fish: Mating with any male they see ensures that these cichlids have a
chance at producing offspring.
2) female Malawi blue cichlid: has a high population but still participates in multiple matings
to avoid inbreeding and increase genetic diversity
3) multiple matings by females may increase the likelihood that they will find a
compatible mate, one that is not sterile, or even help prevent infanticide.
Female Mate Choice
•In most species, females are choosier because females invest more in offspring. females prefer
males with “good genes” (higher chance of offspring survivorship), good parenting, more
resources.
•In most species, females are more likely to provide parental care. Females that carefully select
their mates are at a lower risk of losing their reproductive investment. Selection favors females
that choose males that enhance the likelihood of her offspring's success.
*Although mating is important, it can be a costly event, females are predicted to be
choosier about selecting their mates than males because of risks during mating,
such as aggression or disease transmission, which may negatively impact the
female's reproductive output.
Male Mate Choice
This may seems controversial but male mate choice is important in many mating systems. Male
mate choice occurs most often when males are substantially involved in caring for their o spring,
or when there is great variation in the quality of the females as mates within a population. If
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BIO220H1 Full Course Notes
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