Mate Choice

Mate choice is the process in which one organism chooses another one to mate with. The overall reason for mate choice in any species is to pick a mate that can provide better genetic material that will produce more fit offspring that are more likely to survive and have offspring of their own. Mate Choice is based on the Theory of Natural Selection. Only organisms that are well adapted to survive in the environment that they live in will survive long enough to mate and produce their own offspring, to pass along their traits.

Direct and indirect benefits

Direct Benefits

Direct benefits of choosing mates affect the female directly, such as increasing her own lifetime reproductive output.^[1] Females that choose males that are more able to reproduce with them, then in turn increase the probability of having more offspring that will survive.^[2]

Indirect Benefits

Indirect benefits of mate choice are ones that benefit offspring of the organism making the choice. The organism chooses a mate with a particular favorable trait. This trait is then passed down to its offspring, benefiting the chooser directly. In some fish species, males with eggs already in their nests were preferred over other males who had none. The indirect benefit that can be seen from this example is that more offspring will survive and be able to reproduce because the father is better at watching over the eggs.^[3] Choosing males that already watched over eggs benefitted the mother indirectly because her offspring now had a better chance to survive.

Costs

Mate choice while it has its benefits, can be a costly undertaking involving considerable expenditure of time and energy.^[4] This not only occurs in female mate choice, but in male mate choice as well.^[5] Optimal mate choice involves a tradeoff between the cost of selecting a mate and the benefit gained by mating with a preferred partner.^[6] Costs include time and energy taken to choose the right males. Benefits include having offspring that are more fit to survive and produce their own offspring, and having a mate that could potentially protect these offspring better than others.^[7] Mate choice is relatively costly to female marine iguanas as they spend around 78% of their energy daily towards mate choice. Results also suggest that assessing high quality mates are more costly than assessing lower quality mates. This is due to more time being taken to visit the higher quality mates. Not only was time lost, but also more body mass was lost. In contrast, females that visited these higher quality males showed a strong trend toward producing follicles of smaller size, which is something directly related to offspring survival. Even though a large percentage of energy was used to choose a mate, the females did end up having more fit offspring.

Sexy Sons Hypothesis

The Sexy Sons Hypothesis suggests that females obtain future fitness benefits from mating with males through the inheritance of her son’s of traits.^[8] Because genes are passed down from generation to generation, the probability of offspring to have a trait would increase greatly if one parent or both parents had the trait to pass down. Significant sire effects on egg to adult viability and son’s pre-productive survival, as well as moderate to high coefficients of additive genetic variation for these traits have been found in Dung Beetles.^[9] Beetles who have selected mates with better genetics tend to have offspring that survive longer and are more able to reproduce than those that do not pick mates with genetic quality. This suggests that carefully choosing a mate is beneficial.^[10]

Cryptic Choice

While most mate choice involves choosing of mates before copulation has commenced, cryptic choice involved selection after the organism has mated. Variation in relative male fertilization success is an important source in variance of male reproductive success.^[11] The most prominent method of cryptic female choice is sperm choice, when one male’s sperm is chosen over another male’s sperm to fertilize the female’s eggs. Sperm competition occurs when the ejaculates of two or more males compete for the fertilization of a given set of ova. In contrast cryptic female choice occurs when females themselves bias sperm use in favor of particular males.^[12] Not only do the females control which sperm is used, but also the amount of sperm used. Females use both sperm displacement in which sperm is removed from storage by the incoming ejaculate of a copulating male, and sperm incapacitation where incoming seminal fluids interfere with resident sperm. Sperm dumping is the term used to describe what the females will eventually do to used sperm or unused and unwanted sperm. In the spider: opopae fosuma, there are several specialized muscles for this function. The sperm storage site and the sperm fertilization sites are separated from one another, allowing females to eject sperm with the same genital mechanisms that move stored sperm from the storage site to the fertilization site.^[13] This is primarily a function only exhibited by spiders and also insects.

Male Mate Choice/Sex Role Reversal

There are certain situations in which the male is the one making the mate choice. In Polygynous societies, males mate with multiple females. Males put forth little energy towards mating most of the time because sperm production is easily done and large in quantity. On the other hand females usually put a lot of energy towards mating since eggs take much more energy and are a lot less expendable than sperm, which is constantly produced by the body during a lifetime. Females usually end up taking care of the young, also causing an energy imbalance between the two sexes. This leaves the male better able to transfer genetic material between multiple females in a short amount of time, allowing him to pass his genes to a greater amount of offspring. Other times the number of females are high and the males are limited. In this case as seen in the three spine stickleback, males choose the females because they are the ones who have more of a selection.^[14]

There are many different genetic factors that determine whether or not a male is a favorable mate to choose, or unfavorable. Actual genes cannot be seen when choosing mates, but there are many cues throughout the animal kingdom that help organisms predict the fitness of other organisms, making choosing mates more efficient and more of a knowledgeable decision. Several factors used by a wide variety of animals include: Size of mate, Sounds, Ornaments, Color, and dancing techniques.

Size

Mates will usually choose organisms that are of larger size, excluding those who are smaller for a variety of reasons. Some of these reasons include protection, more dominance, and the ability to pass along those traits to offspring. Size assortive mating is one of the most common mating patterns in nature because of this.^[15] This occurs in a wide range of animals from flatworms to mammals. Size assortive mating may also result from females trying to match size. Prudent mate choice evolves when small mates choosing larger mates would impose significant costs that outweigh the benefits of having a larger mate.^[16] Specific size choice in sexual selection can lead to sexual dimorphism when the choice is only made for one sex.^[17] Male mate choice is also seen when dealing with specific size choice. When presented with large and small potential mates, male pacific blue-eyed fish spent more time and effort with the larger females.^[18]

Sound

Sound is another factor that can determine mate choice. Sound is used not only to choose mates within a specific species, but is often used as a tool for species recognition as well. In North American Tree Frogs, males form aggregations and each male vocalizes from a relatively fixed position during the calling period on a given night. The female then usually moves close to or touches a calling male. The calls of different species are different each in their own ways, for example H. cinera produce unpulsed advertisement calls while H. versicolor readily increases call duration by providing static impulses during the call. This suggests that these calls are used at least partially for species recognition.^[19] Females also preferred calls that were at slightly different frequencies than the normal frequency, around one to two kHz different. Male field crickets use two acoustic signals in the context of mating, one to attract females from a distance and a courtship song when the female comes closer and makes physical contact with the male.^[20] Because of this mate choice can occur at several different points. Females generally prefer the same type of frequency, and when the frequency was changed on them artificially, they lost all interest in the male. This signifies the importance of the song on the attractiveness of the males in this species. Birds are another type of animal in which songs are used for mate choice. In birds, males with a larger repertoire of songs are usually preferred. The Nutritional Strength Hypothesis states that the amount of songs the bird knows is a good indicator of the bird’s quality because the development of the brain regions underlying song learning and production occurs when young birds typically face nutritional and other stresses during post hatch development. Therefore song repertoire length reflects how well the bird fared during the post hatch period, and might reflect how his offspring will fare during the post hatch period.^[21] Results show that even a relatively brief period of undernutrition experienced early in life can affect the outcome of song learning.

Ornaments

Another important factor in mate choice is ornaments and their color. Ornaments come in various different forms, sizes, shapes, and colors. Depending upon the species, the characteristics of the ornaments can be a tell tale sign towards compatibility and favorability. Resistance to disease is a very important gene to pass down to offspring and sometimes this characteristic can be displayed by an ornament. During the breeding season, male red jungle fowls with large combs, a sexually preferred trait, have lower levels of lymphocytes, but greater cell-mediated immunity indicated by a cutaneous hypersensitivity response. Before the breeding season, both lymphocyte proportion and cell-mediated immunity are positively associated with comb length.^[22] A female in making a mate choice obviously wants their offspring to have better immunity against pathogens, so therefore will pick a mate who displays these characteristics over one that does not. Organisms often do not have only one ornament to display. The California Quail has: a crest, cap patch, white band, blue breast, black patch, tan patch, and a brown patch. Females choose their mates in this instance from a combination of different features that differ based upon their personal preference.^[23]

Mate choice copying^[24] is when one organism observes and copies the mate choice of others. This occurs when mate choice is costly. This will increase the probability of a mate being picked since the organism is copying something that a successful mate performed. This allows a trait to spread non genetically. Male deep-snouted pipefish exhibit this characteristic to enhance their own fitness.^[25] Females did not choose based upon observations of other females in this study. There is a higher rate of copying characteristics, than original characteristics being present. Females could not tell the difference between the two.

Human beings also exhibit mate choice. There is substantial evidence that in human mate choice, females directly select males based on male display of both physical and behavioral traits.^[26] In humans, the main form of attractiveness is the face, often the first thing that we look at on another person and one of the only truly exposed parts of the body. The parasite theory of sexual selection, states that men would prefer average and symmetrical faces in women, and that women would prefer largeness of the secondary sexual traits of the male’s face.^[27] There are several other factors that influence human mate choice that have no significance in the animal kingdom. Money is one influence to choose a mate, and in our society it can play a rather large part. More wealthy individuals are usually seen as more able to provide for one’s offspring. There is no such thing as physical money in the animal kingdom. Humans can also judge and measure expressed preferences before we are forced to make any choices via newspaper ads or online dating services.^[28]

• Sexual selection
• Sexual conflict
• Polygyny
• Monogyny
• Cryptic Choice

References

1. ^ Alcock, Jonathon (2009). Animal Behavior, Ninth edition. Integrative and Comparative Biology. ISBN 10.1093/icb/icp058. 
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3. ^ Forsgren, E (1997). "Female sand gobies prefer good fathers over dominant males". Proceedings of the Royal Society 264 (1368): 1283–1286. doi:10.1098/rspb.1997.0177. 
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10. ^ Garcia-Gonzalez, F; Simmons. "Good Genes and Sexual Selection in Dung Beetles (Onthophagus taurus): Genetic Variance in Egg-to-Adult and Adult Viability". PLoS ONE 6 (1). doi:10.1371/journal.pone.0016233. 
11. ^ Edvardsson, M; Göran (2000). "Copulatory courtship and cryptic female choice in red flour beetles Tribolium castaneum". Proceedings of the Royal Society of London 267 (1443): 559–563. doi:10.1098/rspb.2000.1037. 
12. ^ Pilastro, A; Simonato, Bisazza, Evans (2004). "CRYPTIC FEMALE PREFERENCE FOR COLORFUL MALES IN GUPPIES". Evolution 58 (3): 665–669. doi:10.1111/j.0014-3820.2004.tb01690.x. 
13. ^ Burger, M.; Nentwig, Kropf (2003). "Complex genital structures indicate cryptic female choice in a haplogyne spider (arachnida, araneae, oonopidae, gamasomorphinae)". Journal of Morphology 1 (255): 80–93. doi:10.1002/jmor.10048. 
14. ^ Sargent, R; Berghe (1986). Male Mate Choice in Fishes. 
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16. ^ Taborsky, B; GUYER, Taborsky (2009). "Size-assortative mating in the absence of mate choice". Animal Behaviour 77 (2): 439–448. 
17. ^ Howard, R.D.; Martens, Innis, Drnevich, Hale (1998)). "Mate choice and mate competition influence male body size in Japanese medaka". Animal Behaviour 55 (5): 1151–1163. http://bilbo.bio.purdue.edu/~www_eco/faculty/howard/pdfs/medakaMS.pdf.. 
18. ^ Wong, B; Jennions (2004). "Sequential male mate choice in a fish, the Pacific blue-eye <i>Pseudomugil signifer</i&gt". Behavioral Ecology and Sociobiology 56 (3): 253–256. doi:10.1007/s00265-004-0775-8. 
19. ^ Gerhardt, H. C (1991)). "Female mate choice in treefrogs: static and dynamic criteria.". Animal Behaviour.. 
20. ^ Rebar, D; Bailey, Zuk (2009). "Courtship songʼs role during female mate choice in the field cricket Teleogryllus oceanicus". Behavioral Ecology 20 (6): 1307–1314. 
21. ^ Nowicki (2002). "Brain development, song learning and mate choice in birds: a review and experimental test of the "nutritional stress hypothesis"". Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology 188 (11): 1003–1014. doi:10.1007/s00359-002-0361-3. 
22. ^ Zuk, M; Johnsen (1998). "Seasonal changes in the relationship between ornamentation and immune response in red jungle fowl.". Proceedings of the Royal Society of London 265 (1406): 1631–1635. doi:10.1098/rspb.1998.0481. 
23. ^ Calkins, D; Burley (2003). "Mate choice for multiple ornaments in the California quail, Callipepla californica". Animal Behaviour. doi:10.1006/anbe.2002.2041. 
24. ^ Widemo, M (2005). "Male but not female pipefish copy mate choice". Behavioral Ecology 17 (2): 255–259. doi:10.1093/beheco/arj021. 
25. ^ Widemo, M (2005). "Male but not female pipefish copy mate choice". Behavioral Ecology 17 (2): 255–259. doi:10.1093/beheco/arj021. 
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27. ^ Grammer, K; Thornhill (1994)). "Human (Homo sapiens) facial attractiveness and sexual selection: the role of symmetry and averageness". Journal of Comparative Psychology 108 (3): 233–242. PMID 7924253. 
28. ^ Pawłwski, B; Dunbar (1999). "Impact of market value on human mate choice decisions". Proceedings of the Royal Society of London. Series B: Biological Sciences 266 (1416): 281–285. doi:10.1098/rspb.1999.0634. 

External links

• http://science.jrank.org/pages/48592/An-Overview.html