The females are often more showy than the males.
Polyandry is a rare mating system.
Polyandrous species – female has multiple partners
Needs of the young are an important factor constraining evolution of mating systems.
Consider bird species where chicks need a continuous supply of food.
A male maximizes his reproductive success by staying with his mate, and caring for his chicks (monogamy).
Consider bird species where chicks are soon able to feed and care for themselves
A male maximizes his reproductive success by seeking additional mates (polygyny).
Females can be certain that eggs laid or young born contain her genes; however, paternal certainty depends on mating behavior.
Certainty of paternity influences parental care and mating behavior.
Paternal certainty is relatively low in species with internal fertilization because mating and birth are separated over time.
Certainty of paternity is much higher when egg laying and mating occur together, as in external fertilization.
In species with external fertilization, parental care is at least as likely to be by males as by females.
Paternal care by a male jawfish
Sexual Selection and Mate Choice
In intersexual selection, members of one sex choose mates on the basis of certain traits.
Intrasexual selection involves competition between members of the same sex for mates.
Mate Choice by Females
Female choice is a type of intersexual competition.
Females can drive sexual selection by choosing males with specific behaviors or features of anatomy.
For example, female stalk-eyed flies choose males with relatively long eyestalks.
Ornaments, such as long eyestalks, often correlate with health and vitality.
Female choice - Male stalk-eyed flies
Another example of mate choice by females occurs in zebra finches.
Female chicks who imprint on ornamented fathers are more likely to select ornamented mates.
Experiments suggest that mate choice by female zebra finches has played a key role in the evolution of ornamentation in male zebra finches.