Mate Choice | Principles of Biology from Nature Education

contents Principles of Biology 171 Mate Choice Reproduction underlies many animal behaviors. The greater sage grouse (Centrocercus urophasianus). Female sage grouse evaluate males as sexual partners on the basis of the feather ornaments and the males' elaborate displays. Stephen J. Krasemann/Science Source. Topics Covered in this Module Mating as a Risky Behavior Major Objectives of this Module Describe factors associated with specific patterns of mating and life history strategies of specific mating patterns. Describe how genetics contributes to behavioral phenotypes such as mating. Describe the selection factors influencing behaviors like mate choice. page 882 of 989 3 pages left in this module contents Principles of Biology 171 Mate Choice Mating as a Risky Behavior Different species have different mating patterns. Different species have evolved a range of mating behaviors that vary in the number of individuals involved and the length of time over which their relationships last. The most open type of relationship is promiscuity, in which all members of a community can mate with each other. Within a promiscuous species, an animal of either gender may mate with any other male or female. No permanent relationships develop between mates, and offspring cannot be certain of the identity of their fathers. Promiscuous behavior is common in bonobos (Pan paniscus), as well as their close relatives, the chimpanzee (P. troglodytes). Bonobos also engage in sexual activity for activities other than reproduction: to greet other members of the community, to release social tensions, and to resolve conflicts. Test Yourself How might promiscuous behavior provide an evolutionary advantage for males? Submit Some animals demonstrate polygamous relationships, in which a single individual of one gender mates with multiple individuals of the opposite gender. In polygynous relationships, one male mates with multiple females, while in polyandrous relationships, one female mates with multiple males. Polygamy is the most common type of relationship in the animal world. Of the two forms of polygamy, polygyny is far more common than polyandry. Polygynous species range from toads, spiders, and cuttlefish to aardvarks, elks, elephant seals and whales. A single male elephant seal may maintain a harem of 40 or more females, all with whom he mates (Figure 1). Evolutionarily, polygyny increases the opportunities for a dominant male to transmit his genes to future generations through multiple females. Figure 1: Elephant seals (Mirounga leonina). A single male elephant seal may maintain a harem of as many as 40 females. Craig K. Lorenz/Science Source. Polyandry has been observed in a variety of bird species, including Harris' hawks, acorn woodpeckers, spotted sandpipers (Figure 2), and red-necked phalaropes. Tree toads, field crickets, agile frogs, marmosets, bandicoots, pipefish, and a number of other animals also practice polyandry. Among birds in particular, polyandry occurs in two forms: simultaneous and sequential. In simultaneous polyandry, a female maintains more than one nest and acts as a mating partner with more than one male at the same time. In sequential polyandry, a female mates and nests with one male partner after another. Figure 2: A spotted sandpiper (Actitis macularius). Spotted sandpipers display polyandrous behavior. Jim Zipp/Science Source. In a polygynandrous relationship, multiple females and multiple males live and breed together where there are exclusive relationships between two or more males and two or more females. Dragonflies, Eastern box turtles, swallows, warthogs, lions, and Tasmanian devils, among other species, demonstrate polygynandry. Polygynandry has a number of advantages over other types of mating relationships, as males face less competition for mates and younger members of the group receive greater protection. For example, male and female spectacled caimans (Figure 3) breed together before females build their nests, where they guard their eggs and young, together with a male. Figure 3: A spectacled caiman (Caiman crocodilus). Male and female spectacled caimans breed and protect their eggs and young together. Gregory Ochocki/Science Source. Some animal species are monogamous, that is, two animals bond exclusively with each other for an extended period of time. A monogamous relationship may extend over a single mating season or for many years. Some monogamous relationships endure for twenty years or more. Many species favor monogamous relationships, including giant river otters, meerkats, white rhinoceroses, agile gibbons, greater flamingos, Magellanic penguins (Figure 4), mute swans, and shingleback skinks. Human beings often engage in monogamous relationships, although those relationships may take the form of serial monogamy. In serial monogamy, a pair of individuals remain together for an extended period of time before ending their relationship and beginning new monogamous relationships with a different partners. Figure 4: Magellanic penguins (Spheniscus magellanicus). Magellanic penguins mate for long periods of time. There is at least one report of a pair sharing the same nest for 16 years. Art Wolfe/Science Source. Species involved in different kinds of mating relationships have evolved morphological differences known as sexual dimorphisms (Figure 5). These physical differences allow the sexes to differentiate each other. Typical sexual dimorphisms have evolved because males compete with each other for mates, something females rarely do. Therefore, males typically are larger, have weapons of various sorts for use in subduing competitors, and engage in mate-attracting displays as a result of selection for the ability to dominate rivals and attract females. Sexual dimorphisms are most pronounced among species whose mating practices are primarily polygamous and least pronounced among those who practice monogamy. In polyandric species, such as the garden spider, the female generally displays more brightly colored markings than a male. In a polygynic species, the male generally displays the more vivid characteristics: a brighter color, larger size, or more pronounced appendages, as in some beetle species. Figure 5: Mating pairs. (a) Sexual dimorphism in spiders. Male and female black widow spiders (Latrodectus mactans) can vary greatly in size and color. (b) Male and female western grebes (Aechmophorus occidentalis) involved in a courtship dance. Western grebes are monogamous birds with few apparent differences in morphological features. (a) James H. Robinson/Science Source. (b) Phil A. Dotson/Science Source. Test Yourself A familiar sexual dimorphism among ungulates is the presence of large antlers in males. What form of mating system would be expected in species displaying these dimorphisms? Submit As with mating behavior, animals exhibit a wide variety of parenting behaviors. These behaviors appear to be influenced by at least two factors: independence of the young at birth, and certainty of paternity. In some species, a newborn animal is well developed and can take care of itself at a minimal level. For example, most ungulate young stand and walk within minutes of birth, although they rely entirely on their mothers for nourishment. Parental treatment of mammalian young varies widely, depending on the offsprings' stage of development at birth. Marsupials, for example, carry their completely helpless newborns for months in pouches that contain mammary glands. In an even more extreme case, monotremes lay eggs that incubate in a pouch. After hatching, the young are nourished by milk that is secreted into the pouch through the mother's skin rather than through mammary glands. Members of other classes of animals display a similar range of variability in the care of their young. Among reptiles, the young are generally on their own shortly after hatching, although parents may guide the newborn to water if they require an aquatic habitat, or provide some minimal level of protection against predators. For some egg-laying animals, parents provide protection to the eggs themselves. Either parent may carry eggs on its backs, under its skin, or even in its mouth to protect against predators. For example, the female marsupial frog (Gastrotheca) carries her eggs in a brood pouch on her back. In such species, the young are essentially responsible for their own survival once the eggs hatch. Similarly, newborn fish are independent from the moment of birth, so parental care focuses primarily on protecting the eggs. Once thought to be uncommon, parental care among fish is now known to be widespread, with more than 80 families of bony fish demonstrating some form of care for their eggs. In some fish species, parents fan the eggs to provide a continuous supply of oxygen, hide the eggs to protect them from predators, or clean the eggs to remove fungal growth and other contamination. Other fish species build nests in which their eggs can be suspended. These nests lie directly on a lake or pond bottom, suspended in aquatic plants, or are supported by masses of bubbles produced by a parent. In many cases, males are responsible for the care of the eggs. In some cases, this care extends beyond hatching. Male banded jawfish (Opistognathus macrognathus), for example, protect their young by enveloping them in their mouths for a short period of time. Birds have also developed complex systems of parental care for their eggs. Most birds are born helpless, relying entirely on their parents for food and protection for at least a few weeks. In some

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