Why might male orb weaving spiders be less inclined to practice suicidal sex than male praying mantises?

Question

BlackTom AI · Accepted Answer

High local mate availability for orb-weaving males means the fitness benefit of sacrificing oneself to a female is usually outweighed by the lost future mating opportunities.

1) Relevant knowledge points and concepts
- Sexual selection and reproductive strategy: males evolve behaviours that maximize lifetime reproductive success (number of offspring sired).
- Sexual cannibalism and “suicidal” mating: in some species (e.g., many mantids) a male being consumed can increase immediate paternity (longer copulation, transfer of more sperm) or provide female nutrition that boosts offspring survival.
- Opportunity cost and population density: when males are abundant and females are encountered frequently, surviving to mate again is often more valuable than a single high-investment mating (terminal investment is favored when future mating chances are low).

2) Step-by-step reasoning
- If orb-weaving spiders occur at higher population densities, a male’s expected number of future matings is higher than that of a solitary mantis male.
- Dying during one mating eliminates all those future matings, so suicidal sex has a large opportunity cost for orb-weavers.
- For praying mantises (low density, limited mate encounters), the male’s chance of future matings is low; therefore a strategy that increases paternity in a single event (even at cost of death) can be favored by selection.

3) Simple numeric illustration (expected-value logic)
- Suppose a surviving male expects 2 future matings worth 1 offspring each (expected future = 2).
- If suicidal mating yields immediate paternity = 1.5 but causes death, the survivor option (2) > suicidal (1.5), so survival is favored.
- In contrast, if a mantis male expects 0.2 future matings (expected future = 0.2), then dying for 1.5 offspring (1.5 > 0.2) is beneficial.

4) Why the correct answer is correct
- Option b states orb-weaving spiders have higher population density and therefore better chance to mate multiple times. That raises the opportunity cost of suicidal sex, selecting against it. This directly explains why orb-weaving males are less inclined to be cannibalised.

5) Why the other options are incorrect
- a: Claims orb-weaver females are multiply fertilised so cannibalism has no advantage — this is an oversimplification; multiple mating patterns vary and don’t by themselves explain male behaviour as clearly as mate availability/opportunity cost.
- c: Biologically incorrect — male mantises can copulate without the female removing the head; cannibalism sometimes follows mating but is not required for ejaculation.
- d: Females consuming “excess ejaculate” as preferred nutrient source is not supported; the adaptive explanation for cannibalism centers on female nutrition and male paternity trade-offs, not ejaculate consumption.

Conclusion: The reasoning supports option b as correct: orb-weaving spiders’ higher population density gives males better chances to mate again, so suicidal sex is less advantageous. This matches the provided answer.

Why might male orb weaving spiders be less inclined to practice suicidal sex than male praying mantises?Single choice

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