Question

1) Name two species with non-genetic sex determination and describe the effective mechanism

2) Describe the key evolutionary transitions that emerged as sexual organisms transitioned fromunimorphic to dimorphic and how this led to sexual selection. Explain with examples from readings and articles mentioned in class.

please can you explain in both in about 3-4 paragraphs so I could understand more clearer.

Answer 1

1)a.Bonellia Viridis, a marine worm,-It has environment dependent sex determination; sex depends on where the larvae land.Environmental sex determination is the establishment of sex by a non-genetic cue, such as nutrient availability, experienced within a discrete period after conception. This is in contrast to genotypic sex determination, which establishes sex at conception by genetic factors such as sex chromosomes. Environmental sex determination is different to some forms of sequential hermaphroditism in which the sex is determined flexibly after birth.

b.American alligator-(crocodile) It shows temperature-dependent sex determination, , it is the environmental temperature during a critical period of embryonic development that determines whether an egg develops as male or female. This thermosensitive period occurs after the egg has been laid, so sex determination in these reptiles is at the mercy of the ambient conditions affecting egg clutches in nests.

2)monomorphic (of an animal species) having sexes that are similar in size and appearance.Species that are sexually monomorphic show no difference between the two sexes other than their genitalia. They have no secondary sex differences, and no real differences in size, colour, eating habits, etc. This phenomenon is the opposite of sexual dimorphism, where there are marked differences between the sexes.

Dimorphic-Sexual dimorphism is the condition where the two sexes of the same species exhibit different characteristics beyond the differences in their sexual organs. The condition occurs in many animals and some plants. Differences may include secondary sex characteristics, size, weight, colour, markings, and may also include behavioral and cognitive differences.

Darwin noted that sexual selection depends on the struggle between males to access females. He recognized two mechanisms of sexual selection: intrasexual selection, or competition between members of the same sex (usually males) for access to mates, and intersexual selection, where members of one sex (usually females) choose members of the opposite sex.

Sex roles are defined by differences in gametes: females produce relatively few, highly nutritious (usually non-motile) gametes, whereas males produce comparatively abundant, smaller, motile gametes. Because only a single gamete of each type is required to produce an offspring, there will be an excess of male gametes that will not fertilize any eggsIn sexually reproducing species, every offspring has one father and one mother, so the average reproductive success is equal for both males and females.

A successful male can potentially sire many offspring. If a male gains a disproportionate share of reproduction, he will take away reproductive opportunities from other males, leading to a high reproductive variance among males. A successful female, on the other hand, will not take away reproductive opportunities from other females, leading to a smaller variance in reproductive success. The higher the reproductive variance, the stronger the effects of sexual selection . Strong sexual selection typically results in sexually dimorphic traits that are exaggerated, or more elaborate, in the sex with highest reproductive variance .