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LEC.248 > Reproduction > Flashcards

Reproduction Flashcards

1
Q

what is reproduction?

A
  • The process by which individuals (parents) produce new individuals (offspring)
  • Passing on genes: direct fitness
  • A fundamental feature of all vertebrate life
  • Can be sexual or asexual (even in vertebrates)
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2
Q

how many species of vertebrates are known to reproduce asexually

A

> 100

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3
Q

what is the difference between sexual and asexual reproduction

A
  • Sexual: requires combination of male & female gametes
  • Haploid gametes, produced by meiosis, fuse (fertilisation) to form diploid zygote
  • Sexual → genetic variation and adaptability
  • Asexual: requires 1 individual (the mechanism varies)
  • Asexual → if sex unlikely or costly… derived in vertebrates
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4
Q

what is parthenogenesis and what animals do it

A
  • Embryos develop from (haploid) unfertilised eggs, but offspring diploid
  • Method of doubling varies, before/after meiosis, so full or partial ‘cloning’
  • Wild fish, amphibians & reptiles (but in captivity…)
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5
Q

why does parthenogenesis occur?

A
  • Usually facultative e.g. if finding a mate is difficult and is their only option to pass genes on
  • Can be obligate – always takes place
    o e.g. all female desert grassland whiptail lizard
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6
Q

what is Gynogenesis

A
  • Similar to obligate parthenogenesis, but…
  • Sperm needed to induce reproduction
  • Yet no fertilisation
    o e.g. Amazon molly
  • All individuals are female
  • Sperm from mating with males of related species
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7
Q

what has gynogenesis evolved from?

A

hybridisation

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8
Q

what is the difference between Dioecious and Hermaphroditic

A
  • Most vertebrates are dioecious (gonochoric): male & female reproductive organs in separate individuals
  • But some are hermaphroditic: some hagfish, lampreys & amphibians, hundreds of bony fish
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9
Q

what does it mean that an animal can be hermaphroditic simultaneously or sequentially

A
  • Sequential Start as one gender and become a different one later in life
  • Simultaneous – both reproductive organs at same time
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10
Q

what is the difference between Iteroparous and Semelparous

A
  • Most vertebrates are iteroparous: breed multiple times during lifetime
  • Some are semelparous: breed once then die
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11
Q

what is the difference between r and K strategists

A
  • r-strategists:
    ›High reproductive rate
    ›Many offspring
    ›Low offspring survival
  • K-strategists:
    ›Low reproductive rate
    ›Few offspring (often 1)
    ›High offspring survival
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12
Q

what is an example of an extreme r strategist?

A

Coral reef pygmy goby, <20mm
›Shortest living vertebrate: <60 days
›Sexual maturity: 1-2 weeks
›Three clutches of 150+ eggs

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13
Q

what is an extreme example of K strategist?

A

Greenland shark, 2-4m
›Longest living vertebrate: 300+ years
›Sexual maturity: 150 years
›Conservation implications

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14
Q

what is an example of an intermediate of r and K

A

leatherback turtles

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15
Q

describe the difference in internal and external fertilisation

A

External: ancestral, eggs & sperm released in water
o jawless & most bony fish, many amphibians

Internal: all terrestrial species
o some bony fish & amphibians, all cartilaginous fish, reptiles, birds & mammals

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16
Q

what does external fertilisation have large egg/sperm numbers?

A

to maximise:
›Fertilisation success
›Chance of offspring survival

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17
Q

why do males have an intromittent organ for internal fertilisation?

A

– delivering sperm closer
›Maximises fertilisation success
›Often highly specialised: penises

Intromittent organs e.g. claspers and projected pieces at anal fins Snakes have 2 penises – females have 2

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18
Q

Although most birds have lost their intromittent organs, what example still occurs?

A

Lake Duck (Argentine ruddy duck: a 42.5cm corkscrew penis
o Males have developed this to maximise chances to make sure they are the one to fertilise egg – corkscrew to make sure it keeps in place

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19
Q

what is delayed fertilisation and why does it occur?

A
  • But sometimes, females store sperm & delay fertilisation
    ›In extreme cases, for several years e.g. painted turtles
  • Known from all vertebrate groups except jawless fish
  • Female choice, paternity bias
    o Can allocate sperm from different males to fertilise eggs – can bias towards certain males’ sperm they have stored
20
Q

what are the 3 major reproductive modes?

A

Oviparity: Laying eggs

Viviparity: Giving birth to non-shelled (‘live’!) young

Ovoviviparity - aplacental viviparity

21
Q

describe Oviparity?

A

Laying eggs
* Ancestral reproductive mode
* Occurs in all vertebrate groups, including all birds
* Little or no embryonic development in mother
* Embryos nourished by yolk
* Eggs laid in cases in some cartilaginous fish
* Eggs with shells laid in all amniotes

22
Q

describe Viviparity

A

Giving birth to non-shelled (‘live’!) young
* Evolved >140 times independently in vertebrates (Saldívar-Lemus & Macías Garcia 2022 Behav Ecol Sociobiol 76:68)
* Occurs in all vertebrate groups except jawless fish & birds, dominant in mammals
* Internal fertilisation, more stable development – but selective pressures debated
* Embryos nourished by mother – usually via a placenta

23
Q

describe Ovoviviparity

A
  • aplacental viviparity
    ›Retained eggs, embryo nourished by yolk, not mother
    ›Young born after hatching
  • Transitional state in vertebrate evolution
  • Some elasmobranchs, bony fish & amphibians (not reptiles by this definition)
24
Q

describe the characteristics of marsuplials reporduction

A
  • Viviparous, but primitive placenta & short gestation
  • Young born in foetal state
  • Perhaps linked to attack by mother’s immune system- invader so get’s it out sooner so it survives
  • In most, development occurs in a pouch
  • Pouches vary with lifestyle
    o Wombats have backwards facing pouch as it digs a lot
  • Prolonged suckling, so teeth develop late
25
what triggers reproduction?
* The timing of breeding is under hormonal control the hypothalamic-pituitary-gonadal (HPG) axis is involved.
26
what are the three types of breeding?
›Continuous ›Seasonal ›Opportunistic
27
describe continuous breeding
* Uncommon, usually associated with tropics o tropical systems aren’t totally stable but have less seasonal variation than other parts of the world * Stable environments, food availability predictable ›e.g. great apes * But lots of tropical species don’t breed continuously… * And some temperate species do ›e.g. woodpigeon (they have peaks in the year still) Generalists (food and habitat) are more likely to be continuous breeders o also being tolerant to urbanisation is helpful
28
describe seasonal breeding
* Most species experience fluctuating conditions – food, weather etc. * Reproduction is costly, so most only breed when conditions are favourable * Usually timed so offspring born at peak time ›Often annual in temperate zone (spring and summer) ›Timed with rains in tropics
29
what are cues in seasonal breeders?
* Photoperiod a major cue, triggering HPG axis activity Some are ‘long-day’ breeders (e.g. many temperate birds), others ‘short-day’ breeders (e.g. many large temperate mammals) * the young are born at the species peak time * But air or water temperature also important cues * Many fish use lunar reproductive cues – tidal conditions
30
describe opportunistic breeding
* Only breed if & when conditions allow (i.e. conditions unpredictable) * no temporal pattern
31
describe Phenological Mismatch in great tits and caterpillars
peak biomass of caterpillars in the life cycle between hatching and pupae shifts around 2 weeks earlier each year, where as the peak food needed for a great tit shifts only 1 week earlier, so no longer coinciding
32
how can sex be determined?
›Genetic (chromosomal) ›Environmental * Genetic: most species, but highly variable in form * Environmental: common in reptiles, usually temperature- dependent, but can also be exposure to hormones
33
what are mammals sex chromosomes
* Males heterogametic * Males: XY, Females XX * Some bizarre, & poorly understood exceptions o Mole voles: no Y o Grass mice: XX & XY females
34
what are birds sex chromosomes
* Females heterogametic * Males: ZZ, Females ZW * ZZ/ZW have different evolutionary origin to XX/XY * But, embryos are sensitive to oestrogen… o ZZ eggs in chickens can be ‘reversed’ with oestrogen o Unclear if occurs in the wild
35
what are amphibian sex chromosomes
* Lots of different forms of sexual determination * Males & females can be heterogametic * ZZ/ZW & XX/XY both occur * In Rana rugosa, both in a single species! * High sensitivity to sex hormones – reversal possible * Some temperature effects
36
what are reptiles sex chromosomes?
* Highly variable * Genetic: some species in most groups, but still sensitive to temperature * ZZ/ZW & XX/XY both occur * Environmental: some species in all groups, including all crocodilians * Incubation temperature key, but sensitivity to sex hormones occurs too
37
what 3 patterns occur with temperature dependence
›(1) Females produced at low temperatures - crocodiles ›(2) Females produced at high temperatures - turtles ›(3) Females produced at extreme temperatures(rare) – leopard gecko
38
what are the sex chromosomes in fish
* Very poorly known in jawless, cartilaginous & lobe-finned fish * In ray-finned fish – just about anything goes! * ZZ/ZW & XX/XY both occur * Temperature- & hormone- dependence both occur * sex change is widespread: sequential hermaphroditism
39
for sex change, when is the best time to switch?
when male and female trends with number of offspring produced against body size overlap.
40
what is it called when female first, male first
›Female first: Protogyny (Asian sheepshead wrasse) ›Male first: Protandry (clownfish)
41
when is reproductive value greatest for males and females?
* For males the reproductive value is greater when they are younger but in females it is greater overtime
42
what offspring nutrition and care occurs before hatching/birth?
* Vertebrate embryos develop from eggs & have a yolk sac to obtain food (except in amphibians) * In most groups, this contains yolk = a specialised nutrient supply * If oviparous & ovoviviparous, no direct maternal input & yolk large * If viviparous, little or no yolk… placental nutrition
43
what is intrauterine cannibalism
* Widespread in ovoviviparous sharks * Embryos use up their yolk & turn to… * Unfertilised eggs (oophagy) e.g. porbeagle shark * Siblings & half-siblings (embryophagy)
44
what is the offspring nutrition and care after hatching/birth in vertebrates
* Very rare in fish * Rare in amphibians, but egg provisioning occurs in some * Absent in reptiles (?) * Widespread in birds (essential for altricial young) * Widespread in mammals (milk, but after weaning too) * The provision of providing nutrition after birth is relating to endothermy and size (Meiri 2019 Biol J Linn Soc 128:1052)
45
how is lactation under hormonal control?
›Prolactin (production), oxytocin (flow) ›Inhibited by oestrogen/progesterone
46
what is the evolution of lactation
›Removed dependence on yolk ›Ensured a reliable food supply

LEC.248 (5 decks)

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