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In some species, individuals __ during their lifetime; in other species, like sea slugs, an individual is both __ and __.
- change their sex
- male and female
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Other species, like bees, only contain few individuals who can __.
A population outlives its members only by __, the generation of new individuals from existing ones
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a. Two modes of animal reproduction—__and __
i. In sexual: __
a. Female gamete: __
b. Male gamete: __
- sexual
- asexual
- fusion of haploid gametes-->diploid zygote, which gives rise to gametes by meiosis
- egg= large, nonmotile cell
- sperm= smaller, motile cell
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i. Asexual reproduction: __
1. Reproduction relies entirely on __ cell division
b. Majority of animals carry out __, but some have __like the __and __
- generation of new individuals without the fusion of egg and sperm
- mitotic
- sexual
- asexual
- rotifer
- whiptail lizard
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I. Mechanisms of Asexual Reproduction
a. Several among invertebrates
i. Fission: __
ii. Budding: __
iii. Gemmules: __
iv. Two-step processes
1. __
a. If more than one piece grows and develops into a complete animal--> __
Parthenogenesis
- separation of parent organism into two individuals of approx. equal size new individuals arise from outgrowths of existing ones
- Release of specialized group of cells that grow into new individuals (sponges)
- 1. Fragmentation: breaking of the body into several pieces
- 2. Regeneration: regrowth of lost body parts
- reproduction
- asexual reproduction in which an egg develops without being fertilized
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Parthenogenesis
- asexual reproduction in which an egg develops without being fertilized, such as in bees, wasps, and ants
- 1. Progeny either haploid or diploid
- If haploid: offspring develop into adults that produce eggs and sperm without meiosis
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2. Present in every__ species (Komodo dragon)
How did they figure this out?
- 1/1000
- a. Females completely isolated from males of species but still produced offspring
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I. Sexual Reproduction: An Evolutionary Enigma
a. Sex enhances __
b. Case study: half females sexually reproduce; other half asexually reproduced
i. Explain results
- reproductive success for survival
- Asexual offspring increase in frequency; sexual will result in same number at each generation if one offspring a male
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Advantages of sexual:
- Unique combos of parental genes formed during recombination and fertilization --> enhance reproductive success of parents when environmental factors change
- - beneficial gene combinations through recombination speed up adaptation only if rate of beneficial mutations is high and population size is small
- - shuffling of genes may rid population of harmful genes
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Advantage of asexual
good for stable environmental due to perpetuation of successful genotypes
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a. Most animals exhibit __in reproductive activity, often related to __
i. This helps __ -->reproduce only when energy supplied and environmental conditions favor __
- cycles
- changing seasons
- conserve resources
- survival of offspring
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1. Example of reproductive cycles: ewes: 15-17 day cycle
a. __( release of mature eggs) occurs at __of cycle, with the cycle occurring during __
i. Resulting pregnancy= 5 months; birth= __
- Ovulation
- midpoint
- fall/ early winter
- spring
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Reproductive cycles:
a. Controlled by __, which are regulated by __like temp, rainfall, lunar cycles, day length, etc.
b. Seasonal temperature important for reproductionà climate change may __[ex: caribou = timing of migration tied to length of daylight]
- hormones
- environmental cues
- decrease reproductive success
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a. Reproductive cycles also found among animals that produce both ways
i. Water flea produces eggs of two types, one that __; the other needs fertilization to develop; the other __
1. __ occurs with favorable environment and __during times of environmental stress
a. Switch linked to season
- needs fertilization to develop
- doesn't and develops by parthogenesis
- Asexual
- sexual
- season
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Different type of __found among only __ animals.
i. Complex form of parthenogenesis that involves __after meiosis, producing __offspring (whiptail lizards)
1. No males, but __are typical of sexual species of the same genus
a. During breeding, one female of each mating does what?
i. Individual adopts female behavior prior to __, when __levels are high, then switches to male-like behavior after __, when __levels are highest
ii. Ovulation more likely to occur if individual is __
1. Isolated lizards lay less eggs than those that go through motions of sex
a. These views show that parthenogenetic lizards evolved from species having __and still require certain sexual stimuli for max reproductive success
- parthogenesis
- asexually reproducing
- doubling of chromosomes
- diploid
- courtship and mating behaviors
- pair mimics male (alternate roles during season)
- ovulation
- estradiol
- ovulation
- progesterone
- mounted during critical time of hormone cycle
- two sexes
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Reproductive cycles have a different type that is found among only __ animals.
asexually reproducing
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a. Finding partner for sex= hardà adaptations= __:
i. Sessile (stationary) animals (barnacles), burrowing animals (clams), etc.
1. Lacking locomotionà hard to find mateà __
- blurring strict distinction between male and female
- hermaphrodism
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i. __: each individual has both male/ female reproductive systemsà since they have both parts, any two individuals can mate
1. each animal __
2. in some species, hermaphrodites can __= no partner
- Hermaphroditism
- donates and receives sperm during mating
- self-fertilize
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a. Different variation of sexual reproduction in wrasses
i. Live in __with one male and several females
1. When male dies, no sexual reproductionà what happens?
a. Advantage of this: because male defends harem against intruders, a larger size may be more important for males
- harems
- the largest/ oldest female wrasse changes sexes (sex reversal) and makes sperms
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i. Oysters do the same: reproduce as males and then later as females, when their size is greatest
1. Number of gametes produced increases with __, __in this direction maximizes gamete productionà enhanced reproductive success
- size for females more than males
- sex reversal
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a. Fertilization either __(female releases eggs into environment where male fertilizes them) or __(sperm deposited in/ near female reproductive tract)
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External:
i. __habitat almost always required= prevents __ (many aquatic invertebrates)
1. __is crucial for union
- Moist
- gametes from drying out and allowing sperm to swim in eggs
- Timing
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External fertilization:
i. Among some species with external, individuals clustered in same area release gametes into water at same time, called __
1. In some cases, a chemical signal generated by one individual in releasing gametes triggers __
2. In other cases, environmental cues cause __(palolo worm times spawning with season/ lunar cycle)
a. In spring: moon in last quarter, worms break in half, releasing tail segments engorged with sperm or eggsà rise to surface where eggs are fertilized
- spawning
- others to release gametes
- whole population to release at same time
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External i. When not synchronous, specific __leading to fertilization of eggs of one female by one male may occur
1. “__” behavior benefits
:__
- mating behaviors
- courtship
- Allows mate choice and, by triggering release of both eggs and sperm, increases probability of successful fertilization
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Internal
i. Sperm reaches egg, even in dry environment
ii. Requires __that leads to __, as well as sophisticated and compatible reproductive systems
1. Male copulatory organ __; Female reproductive tract has receptacles for __ and __ of sperm to mature eggs
- cooperative behavior
- copulation
- delivers sperm
- storage and delivery
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a. __ (chemicals released by one organism that can influence physiology and behavior of other individuals of the same species) may be used, regardless of type of fertilization
i. Small, __that disperse into environment and are active in tiny amounts
ii. Function as __, enabling some female insects to be detected by males from far away
- Pheromones
- volatile or water-soluble molecules
- mate attractants
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Internal Fertilization Pros:
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- a. Pros: production of fewer gametes; survival of higher fraction of zygotes
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Internal fertilization:
i. Better zygote survival due to fact that eggs fertilized __are sheltered from __
1. associated with mechanisms that provide __and __
- internally
- predators
- greater protection of embryos
- parental care of the young
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Internal Fertilization:
a. rather than secreting a protective eggshell, some animals retain the __for a portion of its development within __
i. embryos of marsupials=__
ii. embryos of (placental) mammals= __
- embryo
- female reproductive tract
- short period in uterusàembryos crawl out and complete fetal development attached to mammary gland in mom pouch
- remain in uterus throughout where they are nourished by mom’s blood supply through the placenta (temp. organ)
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a. When eggs hatch or human born, they aren’t yet capable of __
i. Instead adult birds feed young and mammals nurse offspring
b. __widespread (invertebrates do it too)
i. Among vertebrates, some frogs carry tadpoles in stomach until they undergo metamorphosis and hop out mouths
- independent existence
- Parental care
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a. Sexual reproduction in animals relies on sets of cells that are precursors for __
i. Group of cells dedicated to this is often established very early in __and remains in __ state while plan develops
1. Cycles of growth and mitosis then increase (__) the number of cells that can __
- eggs and sperm
- formation of embryo
- inactive
- amplify
- make eggs or sperm
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a. In producing __from the __and making them available for __, animals employ a variety of reproductive systems
i. Simplest don’t __ (organs producing gametes in animals)
1. Palolo worms= separate sex but no distinct gonads; rather, eggs and sperm develop from __
a. As gametes mature, they are released from body wall and fill the __
- gametes
- amplified precursor cells
- fertilization
- discrete gonads
- undifferentiated cells lining the coelom
- coelom
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1. Depending on species, mature gametes may be shed through __, or swelling of mass of eggs may __
- excretory opening
- split portion of body open, spilling eggs into environment
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i. More complex include sets of __ and __that carry, nourish, and protect gametes and sometimes the developing embryos
accessory tubes and glands
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1. Most insect species have separate sexes with complex reproductive systems
a. In males: __develops in _ and pass along __to two seminal vesicles for __
i. During mating, sperm __ into female tract
1. There, __develop in pair of __and are conveyed through __to __
a. Eggs are fertilized in __and expelled for development __the body
- sperm
- testes
- coiled duct
- storage
- ejaculates
- eggs
- ovaries
- ducts
- uterus
- uterus
- outside
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a. In many insects, female reproductive system includes one or more __, sacs where sperm is stored for long periods
i. Because female releases male gametes from the __only in response to __, fertilization occurs under conditions suited to __
- spermathecae
- spermathecae
- appropriate stimuli
- embryonic development
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a. Basic plans of all vertebrate reproductive systems are similar, but vary
i. Nonmammalian vertebrates
1. Digestive, excretory, and reproductive systems have common opening to outside (__)
cloaca
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i. Mammals
1. Lack __and have separate opening for __and __and __systems
a. In most vertebrates, __partly or completely divided into __chambers
b. In humans and other mammals that produce one or few young at a time, birds, and snakes, __is single structure
2. Male reproductive systems differ in __organs
a. Nonmammalian vertebrates, including all reptiles and amphibians, lack a well-developed __and ejaculate sperm by __
- cloaca
- digestive tract
- excretory
- reproductive
- uterus
- two
- uterus
- copulatory
- penis
- turning the cloaca inside out
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a. Although fertilization involves union of single egg and sperm, animals may mate with more than one member of the other sex
i. __: sex of only two individuals ; rare among mammals
1. Mechanisms evolved that enhance __
- Monogamy
- reproductive success of a male with a particular female and diminish the chance of that female mating successfully with another partner
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