Exercises: Types and structures of reproduction

Differentiate between asexual and sexual reproduction in terms of the number of parents, genetic variability of the offspring, and reproduction rate, indicating an advantage of each type.

Name two types of asexual reproduction (for example, binary fission, budding, or fragmentation), an organism that uses them, and the distinguishing feature of each.

Define internal and external fertilisation and explain the difference between oviparous, viviparous, and ovoviviparous animals, providing an example of each.

Explain what a gamete is and two differences from a somatic cell (chromosome complement, function), discussing why gametes cannot have the same complement as the rest of the cells.

Distinguish between oviparity and viviparity with two examples of each, and point out one advantage and one disadvantage of each strategy (protection of the embryo versus the parent's energy investment).

What is courtship? Give two examples (the peacock's tail, birdsong, the bellowing of the deer) and explain its functions (recognising the species, selecting a mate, synchronising reproduction).

Explain what parental care is and describe three different forms (incubation of eggs, feeding of the young, defence of the territory or carrying of the young) with an animal example of each.

Distinguish between direct and indirect development with an example of each (a mammal and a butterfly or an amphibian), and indicate what the existence of a larval phase implies in the life of the animal.

Compare the reproductive strategy of an amphibian and a reptile: type of fertilisation, egg structure, and site of development, highlighting what innovation the amniotic egg represented for the colonisation of land.

Earthworms and snails are hermaphrodites. Explain what this means, what advantages it offers to animals with low mobility, and why, despite this, they usually cross-fertilise with another individual rather than self-fertilise.

Describe the metamorphosis of a frog from egg to adult, indicating the most important anatomical and physiological changes and their relationship to the transition from an aquatic to a terrestrial environment.

A starfish can regenerate an arm, and a planarian cut in two gives two individuals. Explain what relationship there is between this capacity for regeneration and asexual reproduction by fragmentation, and discuss why vertebrates, with such specialised bodies, cannot reproduce this way.

The reproductive cycle of amphibians remains tied to water: gelatinous spawn, external fertilisation and aquatic larvae. Explain this dependence and why many species return to the same pond every year (philopatry), as well as the risk posed by the disappearance of water points.

What is sexual dimorphism? Give two examples (the antlers of the deer, the colours of birds, the lion's mane) and relate it to sexual selection: competition between males and mate choice by females.

Many corals release their gametes on the same night of the year, synchronised with the moon and the tides. Explain what advantage this mass synchronisation has in animals with external fertilisation and which environmental signals can guide it (photoperiod, temperature, the lunar cycle).

The rutting season of many mammals occurs on very regular dates. Explain how the photoperiod (day length) regulates the breeding season and discuss what advantage scheduling births for spring has (food, temperature, time to grow before winter).

A naturalist claims: "To restore the fauna of a degraded wetland subject to unpredictable droughts, it is preferable to introduce K-selected species rather than r-selected species, since, by caring for their offspring, they ensure an extremely high survival rate and will reach a viable population sooner." a) Reasonably refute the naturalist's claim using the concepts of biotic potential, carrying capacity ($K$), and survivorship curves. b) Predict how the population size of an r-selected species versus a K-selected species will evolve if, two years after their introduction, an unexpected catastrophic drought occurs.

On an oceanic island newly emerged after a volcanic eruption, two species of herbivorous insects are accidentally introduced: a solitary female of species A (which reproduces by obligate parthenogenesis) and a pair (male and female) of species B (obligate amphimictic sexual reproduction). a) Predict the demographic dynamics and the rate of colonization of both populations during the first 10 generations in an environment without competition or predators. b) In generation 15, a lethal pathogenic fungus colonizes the island. Justify which population will be more likely to go completely extinct and which will be able to present resistant individuals. c) Based on the above, reason the paradox of the "twofold cost of sex": if parthenogenesis allows a population to grow twice as fast by not producing males, why is sexual reproduction predominant in multicellular animals?

A palaeontology team discovers the fossils of a new primitive Carboniferous tetrapod. Its skeleton lacks copulatory structures, and masses of thousands of tiny fossilised unmineralised shell-less eggs have been found alongside the fossils in sediments from a river floodplain. A researcher on the team claims that this animal already exhibited fully terrestrial reproduction independent of water. a) Refute the researcher's hypothesis by pointing out the physical and cellular impediments (gametic desiccation, sperm motility, and zygote osmoregulation) that make external fertilisation unviable on dry land. b) Justify which anatomical and physiological evolutionary innovations in the gametes and the egg were necessary for amniotes to become independent of the aquatic environment for reproduction. c) Predict what differences you would expect to find in the yolk volume of the ova and in the number of gametes produced per cycle between this fossil and a terrestrial reptile of similar size.

In most vertebrates, males compete intensely for females, and it is the females that choose a mate based on ornaments or courtship displays. However, in seahorses and pipefish, it is the females that actively compete for access to males and display more conspicuous colouration patterns. a) Apply Robert Trivers' parental investment theory to justify why the usual sex roles are reversed in these species. b) The female takes only two days to mature a new batch of eggs, whereas the male requires between two and four weeks to incubate the embryos in his brood pouch. Predict how this difference will affect the operational sex ratio (the proportion of males and females ready to mate at a given time) and which sex will act as the limiting resource. c) Design a simple laboratory experiment to test whether male seahorses prefer to mate with larger females.

Two closely related bird species in two distinct habitats are compared:

• Species 1: Altricial chicks (born blind, naked, and thermodependent) in an environment where food is scarce and evenly distributed throughout the territory.

• Species 2: Precocial or nidifugous chicks (walk and feed on their own within a few hours of hatching) in an environment where food patches are very rich and concentrated in discrete spots easily defendable by a vigorous male.

1. a) Reasonably predict the most likely mating system (monogamy or polygyny) for each of the two species, linking the need for biparental care and the ability to monopolise resources. b) Imagine that a habitat disturbance for Species 1 causes food to become superabundant around the nests, such that a single female is capable of feeding the entire brood without assistance. Predict how the mating system of that population might change in the long term and justify your answer.

Compare three marine species subject to commercial fishing: the hake (Merluccius merluccius, a bony fish that releases between 100 000 and several million pelagic eggs per year without any parental care), the small-spotted catshark (Scyliorhinus canicula, an oviparous shark that attaches about 80 to 100 leathery egg capsules to the seabed), and the starry smooth-hound (Mustelus asterias, a placental viviparous shark with a gestation period of 10 to 11 months that gives birth to between 4 and 15 fully developed pups). a) Analyse the evolutionary trade-off between the number of offspring and the energetic investment per gamete and embryo in these three species. b) Predict which of the three populations will suffer a faster collapse and take more decades to recover if intensive fishing decimates 80 % of reproductive adults. Justify your answer based on sexual maturity, fecundity, and intrinsic rate of increase. c) From an adaptive standpoint, reason what advantages and disadvantages retaining embryos internally entailed for viviparous sharks compared to the ancestral mass spawning strategy.

A conservation centre manages a captive population of an endangered mammal composed of only four individuals: Male 1 and Female 1 (full siblings captured from wild population A), Male 2 (originating from an isolated population B), and Female 2 (daughter of Male 1 and Female 1). Cases of juvenile cataracts of autosomal recessive genetic origin have been recorded in population A. a) Genetically justify why a planned cross between Male 1 and Female 2 would pose an unacceptable risk to the viability of the litter, using the concepts of inbreeding coefficient and inbreeding depression. b) Design the optimal breeding plan among these four individuals to minimise the homozygosity of deleterious alleles and maximise the genetic diversity of the next generation. c) A member of the team suggests solving the lack of breeders by repeatedly cloning Male 2, who shows exceptional health and size. Reasonably argue why this proposal does not solve the long-term conservation problem of the species.

Only two living females of the northern white rhinoceros (Ceratotherium simum cottoni) survive in the world, both unable to carry a pregnancy to term. However, cryopreserved semen from several deceased males and related females of the southern white rhinoceros subspecies are available in zoos and reserves. a) Design a sequential biotechnological protocol (from obtaining biological material to the birth of a calf) to rescue the subspecies using assisted reproduction techniques such as transvaginal ovum pick-up, intracytoplasmic sperm injection (ICSI), and embryo transfer to surrogate mothers. b) Justify why conventional artificial insemination is not applicable in this situation and what biological relevance the cryopreservation of the gamete bank has for the conservation of the species' allelic diversity. c) If three live calves originating from a single male and a single female are achieved through this strategy, critically assess the biological viability of reintroducing this new lineage into the wild without crossbreeding it with the southern white rhinoceros.