Optimality and Fish Reproduction Example

What is optimality in evolutionary trade-offs?

Optimality involves maximizing the benefits of evolutionary trade-offs, particularly in fecundity.

How is age estimated in some species?

Age is estimated using otoliths' daily growth rings.

What challenge does studying long-lived species pose?

Normal mark and recapture methods are not feasible, requiring molecular techniques.

Why is age at maturity a crucial factor in life history evolution?

Before maturity, strong natural selection favors survival, while after maturity, aging begins.

What are the benefits of delayed reproduction?

Older parents produce higher-quality offspring and may have more due to increased body size.

What is the advantage of early reproduction?

Early reproduction reduces the risk of dying before reproducing and shortens generation time.

How is generation time related to evolutionary fitness?

Shorter generation times allow for faster reproductive cycles, similar to compound interest growth.

What is a semelparous species?

A semelparous species has a single reproductive episode before death.

What is an iteroparous species?

An iteroparous species undergoes multiple reproductive cycles throughout its life.

Why do iteroparous species conserve energy?

They must survive for multiple reproductive cycles, balancing investment in survival and reproduction.

What is the significance of clutch size in life history evolution?

Optimal clutch size follows a quadratic function, balancing maximum and minimum numbers.

How does Lack's hypothesis test optimal clutch size?

If birds lay the optimal clutch, both larger and smaller clutches should have lower fitness.

How does brood size impact parental investment?

Larger broods require more resources, while single-offspring (semelparous) parents commit all energy to one.

What is the optimal investment strategy in reproduction?

Organisms balance survival maintenance with reproductive output, shifting strategies depending on environmental conditions.

How do short-lived birds invest in their offspring?

They invest more per offspring, producing larger eggs to maximize fitness.

How does perceived environmental threat affect reproductive investment?

Organisms increase reproductive investment when sensing threats, as seen in fleas exposed to predator cues.

How does mortality risk influence reproductive strategies?

Species in high-mortality environments tend to reproduce earlier and invest more per offspring.

How does body mass correlate with lifespan?

Higher body mass generally equates to longer lifespans.

What was observed when researchers manipulated mortality in lab populations?

Increased mortality led to increased reproductive investment.

Why is lab-based aging research not directly applicable to wild populations?

Lab environments lack natural threats like predation, altering natural selection pressures.

What does "life history" mean in the context of fish biology?

Life history refers to the set of reproductive strategies and traits an organism develops to maximize reproductive success. This includes age at first reproduction, offspring size and number, lifespan, and aging.

How can fish life history traits be plastic?

Fish life histories can change due to environmental pressures, including anthropogenic factors like overfishing. They adapt their reproductive strategies to maximize survival and reproductive success.

Provide examples of life history variations in fish.

Discus fish provide parental care by feeding young with mucus. Manta rays are viviparous (giving birth to live young). Many sharks also exhibit viviparity.

What does it mean for salmon to be anadromous?

Anadromous salmon migrate from freshwater to the ocean for feeding, then return to freshwater to spawn. This strategy helps produce larger, healthier offspring.

What is the difference in reproductive investment between anadromous and resident salmon?

Anadromous fish invest heavily in reproduction but often die after spawning (semelparous species like Pacific salmon). Resident fish reproduce multiple times over several seasons with lower investment per spawning event.

What are precocious males in salmon populations?

These are small males that do not migrate to sea but sneak in during spawning to fertilize eggs, avoiding competition with larger males. They contribute 40-50% of fertilizations.

How does fishing pressure influence fish life history?

Overfishing removes older, larger fish, leading to earlier maturation in populations. This change may be due to plasticity (temporary shift) or evolution (genetic change favoring early maturity).

How can scientists distinguish between plasticity and evolution in fish maturation?

By tracking reaction norms, which show how a genotype expresses different phenotypes across environments. If reaction norms shift over generations, it suggests an evolutionary response.

What types of hermaphroditism exist in fish?

Sequential Hermaphroditism: Changing sex based on size (e.g., clownfish: male to female; wrasses: female to male). Simultaneous Hermaphroditism: Being both sexes at once, common in deep-sea fish.

How do human activities influence fish gender?

Chemical pollutants (e.g., estrogen from contraceptives) can cause feminization of male fish, potentially reducing breeding males and affecting population genetics.

What happens when male fish are feminized due to pollutants?

In most cases, populations remain viable despite some feminization. However, in extreme cases (e.g., Canadian experimental lakes), severe feminization led to extinction in flathead minnows.

What are the major conclusions about fish life histories?

Life history traits are highly variable and adaptive. Fish reproductive strategies impact population genetics. Human activities, including fishing and pollution, significantly alter fish life histories.