Sexual conflict

[5] Interlocus sexual conflict reflects interactions among mates to achieve their optimal fitness strategies and can be explained through evolutionary concepts.

For example, the Neotropical spider, Paratrechalea ornata, displays nuptial gift-giving behaviors during courtship as a part of their male mating efforts.

It is important to note that females also benefit from high fecundity, and thus this trait is probably more affected by classical natural selection.

Sexual antagonism represents an evolutionary conflict at a single or multiple locus that contribute differentially to the male and female fitness.

[14] The retention of such antagonistic alleles in a population could also be explained in terms of increase in the net fitness of the maternal line, for example, the locus for male sexual orientation in humans was identified on subtelomeric regions of X chromosomes after studies conducted on 114 families of homosexual men.

[15] An evolutionary model explained this finding in terms of increased fertility of the females in maternal lines, hence adding to net fitness gain.

The XY, XX and ZW, ZZ system of sex determination allows accelerated fixation of alleles that are sex-linked recessive, male-beneficial and female-detrimental due to constant exposure to positive selection acting on heterogametic sex (XY, ZW) as compared to purifying selection removing the alleles only in homozygous state.

[19] Interlocus sexual conflict involves numerous evolutionary concepts that are applied to a wide range of species in order to provide explanations for the interactions between sexes.

For example, females may behave in ways that are considerably biased towards mating and fertilization success due to the attractiveness of males who exhibit a deceptive or exaggerated secondary sex characteristic.

The study concluded that this behavior is caused by female resistance and not due to a general preference for larger body size males.

[5] Sperm competition is an evolutionary concept developed by Geoff Parker (1970) and describes a mechanism by which different males will compete to fertilize a female's egg.

Physiological adaptations may consist of toxic sperm or other chemicals in the seminal fluid that delays a female's ability to remate.

Higher levels of sperm competition were correlated to larger accessory reproductive glands, seminal vesicles, and interior prostates.

This may include: a) longevity reduction, b) distortion in feeding behaviors (which could increase food intake as seen in Drosophila fruit flies) c) increased risk of infection, d) wound repair through energy consumption,[25] e) male manipulation of female reproductive schedules,[26] f) susceptibility to predators,[9] and g) reduced female immune response.

[9] Sexual conflict over mating can cause hermaphrodites to either cooperate or display aggressive behavior in the context of gender choice.

This behavior is costly to both sides, and counter-adaptations have evolved in the affected sex ranging from cooperative defense of their young to loss minimization strategies such as aborting existing offspring upon the arrival of a new male (the Bruce effect).

Traumatic insemination describes the male's tactics of piercing a female and depositing sperm in order to ensure paternity success.

[34] Female bed bug mortality rate due to traumatic insemination could be related more to STDs rather than just the open wound.

[37] This cost of mating in D. melanogaster females is not due to receipt of sperm but is instead mediated by accessory gland proteins (Acps).

The mating plugs of Drosophila hibisci are gelatinous, hard composites that adhere to the uterus of the female in the event of copulation.

A study tested two hypotheses concerning mating plugs: a) that they were nutritional gifts for females to digest to provide maintenance of the eggs during maturation, or b) that they could serve as a chastity device to prevent sperm of rivals.

The study found that mating plugs had no effect on female nutrition and serve as an enforcement device against rival males.

[46] Forced copulation (sexual coercion) by males occurs in a wide range of species and may elicit behaviors such as aggression, harassment and grasping.

When the male Malabar ricefish is ready to copulate, he dashes at high speed towards the female and release his club-shaped organ, the gonopodium also known as an anal fin.

[9] Examples of species with grasping traits are water striders, diving beetles, and the dung fly Sepsis cynipsea.

[47] In water strider Gerris odontogaster, males have an abdominal clasping mechanism that grasps females in highly complex struggles before mating.

[49] Male water striders Gerris odontogaster have grasping structures that can prolong copulation depending on the size of their abdominal processes.

This means that females kill and consume males, sometimes after sperm exchange, in order to enhance the quality and number of her offspring.

The presence of a nuptial gift by a male increases the proportion of sperm retained by the female (With copulation duration controlled for).

[9] In Remiz pendulinus, the Eurasian penduline tit, the male will build an elaborate nest and may or may not be joined by a female at any stage of construction.