Costs to Females
Costs of MatingIt is commonly seen that mating involves costs to both males and females. One of these costs, elevated predation risk to females, plays a role in structuring mating systems (Gwyne, 1989). Harassment of females by males may also pose a cost to females, as such, multiple matings may be favored (Rowe, 1992). Mating itself may pose a threat to females and as such reduced mating may be favored (Rowe, 1994). The mating process in the water strider poses many costs to the female.
When searching for a mate, mating behaviors of males increase the risk to females by many components :
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Image 6: demonstrating male guarding , copulation and a single female (Adapted from Han et al., 2007 :http://journal.behecolpiotrsangim.org/2007/ws_sexratio/full_ws.htm)
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Cost of HarassmentFemale water striders often try to avoid males by skating from the area (Rowe, 1992) .The effort and increased movement rates females exhibit when trying to escape a searching males attracts predators and hence the chance of being preyed upon (Rowe, 1994). Furthermore, females who escape and find refuge off the water are unable to feed (Sih and Watters, 2005).
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Costs of Mate ChoiceRowe (1994) showed that the mechanism of mate choice, where reluctance of females to mate with an undesirable male increases the risk of being preyed upon. During these mating battles, females also expend 200% more energy than females who were left alone (Watson et al., 1998). This increased movement also attracts more predators to the scene (Rowe, 1994).
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Mating CostsPredators were seen to prey more efficiently on mating female water strider. Usually, gerrids leap off the water surface or skate away when under attack from predators (Rowe, 1994). Fairbain (1993) showed that female mobility is decreased when carrying males, this increases the risk of predation.
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