Q.101 Behavioral studies on animals have shown that there is relationship between mechanism of reproduction
and male parental care (protecting eggs or the young ones). In aquatic invertebrates, fishes and amphibians for example,
the species that practice internal fertilization rarely show male parental care while a majority of species that practice
external fertilization tend to exhibit male parental care. This is likely due to
(A) the male sex in species that practice internal fertilization are unable to defend against the predators
(B) the male sex in species that practice internal fertilization live on female as parasite
(C) the fact that the females of species that practice external fertilization die soon after laying the eggs
(D) the certainty of paternity in species that practice external fertilization and this behavior is reinforced over generation by natural selection
The correct answer is (D) the certainty of paternity in species that practice external fertilization and this behavior is reinforced over generation by natural selection. In external fertilization, males can guard eggs/young at the fertilization site, ensuring high paternity confidence, which favors male parental care evolution via natural selection.
Option Analysis
(A) Males Unable to Defend in Internal Fertilization
Incorrect. Internal fertilization species (e.g., seahorses) often show male care (pregnancy), disproving defense inability. The pattern holds across capable species; it’s about paternity assurance, not physical limits.
(B) Males Live on Female as Parasite
Incorrect. No such parasitism exists in studied species. Males don’t reside on females post-mating; this misrepresents gamete delivery in internal fertilizers like sharks.
(C) Females Die After Laying Eggs in External Fertilization
Incorrect. Most external fertilizers (e.g., most fish, amphibians) have surviving females that could care but don’t; males do. Semelparity (death post-spawning) is rare, not the driver.
(D) Certainty of Paternity in External Fertilization
Correct. External fertilization allows males to guard eggs immediately post-release, minimizing sperm competition and ensuring offspring relatedness (r≈1). Natural selection reinforces guarding as it boosts inclusive fitness; internal fertilization lowers paternity certainty (female control), reducing male investment incentive.
| Fertilization Type | Paternity Certainty for Male | Typical Male Care? | Example |
|---|---|---|---|
| External | High (site guarding) | Yes | Fish, frogs |
| Internal | Low (female tract) | Rare | Invertebrates |
In behavioral ecology, the mechanism of reproduction strongly links to male parental care, especially in aquatic species where external fertilization correlates with males protecting eggs/young, driven by certainty of paternity and natural selection reinforcement.
Paternity Drives Care Evolution
External fertilization lets males guard gametes at the site, achieving near-100% paternity and favoring care (e.g., nest-guarding fish). Internal fertilization hides eggs in females, reducing male confidence and investment.
Why Other Explanations Fail
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Defense inability: False; capable males still avoid low-paternity scenarios.
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Female death: Rare exception, not rule.
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Parasitism: Non-existent.
This pattern, seen in 30+ fish care origins, highlights evolutionary trade-offs for biotech/genetics researchers studying parental strategies.
