n Flashcards
What is a sex ratio?
The ratio of males to females in a population.
What determines sex ratios in organisms?
Factors like the temperature, food availability, social context, haplodiploidy, and chromosomal systems (XY, ZW).
How does temperature affect sex ratios in reptiles like leopard geckos?
In temperature-dependent sex determination, pivotal temperature produces a 1:1 sex ratio.
How does social context affect sex ratios in fish?
In protogynous species like the blue groper, all start female-largest individuals change into males, skewing sex ratio toward females.
What is the haplodiploidy and how does it affect sex ratios?
In bees, ants, and wasps, unfertilized eggs become males (haploid), and fertilized become females (diploid), allowing queens to control sex ratio.
What are the XY and the ZW sex determination systems?
XY: males are XY (heterogametic), and the females are XX
ZW: females are ZW (heterogametic), and males are ZZ.
Should chromosomal systems always produce a 1:1 sex ratio?
Ideally yes, but actual sex ratios may vary depending on life stage and environmental factors.
What is the Primary Sex Ratio
The ratio at conception (zygote stage); expected to be 1:1 in XY systems.
What is the Secondary Sex Ratio?
The ratio at birth or hatching
What us the Adult Sex Ratio (ASR)?
Ratio of all adult males to females in a populatiopn.
What is the Operational Sex Ratio?
The ratio of sexually available males to sexually available females.
What does the Trivers-Willard Hypothesis state?
When the producing sons and daughters have different costs and benefits, parents will bias offspring sex to maximise fitness.
What are sons more costly in many mammals?
Males are often larger (sexual dimorphism) and polygynous, needing more resources to be successful.
What are the reproductive benefits for daughters vs. sons in polygynous species?
Almost all daughters reproduce; only high-quality males do, so sons are high-risk, high-reward investment.
What might be a physiological mechanism for mammalian sex-ratio manipulation?
Circulating glucose levels may influence embryo development-higher glucose favours male development.
What evidence supports glucose influencing sex ratios?
Diabetic mice have more sons; low-glucose females have more daughters.
Are males more costly to produce in humans?
Yes - many males grow faster in utero, weigh more at birth, and require more maternal energy.
What did Tamini et al. (2003) find about maternal energy use?
Pregnant women carrying boys consumed 10% more energy than those carrying girls.
What did Helle et al. (2002) find about having sons in pre-industrial Finland?
Women who had more sons lived shorter lives; daughters increased maternal lifespan.
What social factor might explain why daughters increase maternal lifespan?
In traditional societies, daughters help mothers with “female” labour tasks.
What did Hurt et al. (2006) find in Bangladesh?
Survival of sons - not just birth - was negatively correlated with maternal lifespan.
What did jasienska et al. (2006) find in rural poland?
More children (sons or daughters) decreased maternal lifespan, but fathers with more daughters lived longer.
What is the Unguarded X hypothesis?
Males (XY) may be more vulnerable to harmful X-linked mutations, leading to shorter lifespans.
What is the Unguarded Z Hypothesis?
In ZW systems, heterogametic females (ZW) may be more vulnerable, paralleling the x hypothesis.
