Chapter 46: ANIMAL REPRODUCTION

There are two principal modes of animal reproduction. Asexual reproduction is the creation of new individuals whose genes all come from one parent without the fusion of egg and sperm. In most cases, just mitotic cell division w/o meiosis & syngamy. {fission, fragmentation, budding, parthenogenesis …} Sexual reproduction is the creation of offspring by the fusion of haploid gametes to form a diploid zygote. Gametes are formed by meiosis. The female gamete, the ovum (unfertilized egg), is usually a relatively large and nonmotile cell. The male gamete, the spermatozoon, is generally a small, motile cell. Chapter 46: ANIMAL REPRODUCTION Many aspects of animal form and function can be viewed as adaptations contributing to reproductive success. Individuals are transient. A population transcends finite life spans only by reproduction, the creation of new individuals from existing ones. Sexual reproduction increases genetic variability among offspring by generating unique combinations of genes inherited from two parents. Sexual reproduction may enhance the {long-term} reproductive success of parents when environment changes or offspring disperse or pathogens evolve. {but there are short-term costs of sexual recombination: males & meiosis}

In a population of parthenogenetic females cloning selves: the pop. can produce babies faster – everyone’s a mom; & each baby reproduces 100% of a mom’s genes, not 50%; Why sex and recombination?Barton NH, Charlesworth BSCIENCE 281 (5385): 1986-1990 SEP 25 1998. Abstract:Most higher organisms reproduce sexually, despite the automatic reproductive advantage experienced by asexual variants. But babies, families & the pop genetically more homogeneous; less variable ecology, more vulnerable to coevolving parasites This implies the operation of selective forces that confer an advantage to sexuality and genetic recombination, at either the population or individual level. The effect of sex and recombination {combining isolated beneficial mutations at} different genetic loci, which increases the efficiency of natural selection, is likely to be a major factor favoring their evolution and maintenance. … With sex, isolated mutations at diff loci in diff individuals can be combined in one individual: beneficial mutations can interact synergistically & deleterious mutations can be purged in batches – both processes can speed adaptation and select for sexual recombination. See: http://www.pbs.org/wgbh/evolution/sex/advantage/index.html

Daphnia: Asexualreproduction occurs in good conditions, early in the season. Females produce clonal parthenogenetic female offspring. Sexualreproduction occurs during adverse environmental conditions: food shortages & end of season. Some males develop from parthenogenetic eggs and some females produce darker eggs that require fertilisation by the males. {males made only when times are tough & sex is apparently a good idea!} The fertilized eggs form dormant ephippia: resistant to freezing, desiccation and digestion and may remain viable in sediment for years, - disperse through time & space. Animals may reproduce asexually or sexually exclusively, or they may alternate between the two modes. {“alternation of generations”} In aphids, rotifers, and the freshwater crustacean Daphnia, X each female can produce eggs of two types, depending on environmental conditions such as the time of year.

The importance of sexual and asexual reproduction in the recent evolution of Allium vinealeCeplitis A. EVOLUTION 55 (8): 1581-1591 AUG 2001 Abstract:In the weedy plant species Allium vineale (wild garlic), individuals may simultaneously produce sexually and asexually derived offspring, by seed and bulbils, respectively. In this study, genetic and genotypic diversity was determined in samples from 14 European A. vineale populations using nuclear (RAPD) and cytoplasmic (PCR-RFLP of cpDNA) markers to investigate the importance of the different reproductive modes. … Genotypic diversity was significantly lower than expected under free recombination in almost all populations, indicating that recruitment into populations is mostly by asexually produced offspring.Nevertheless, … many … genotypes have originated by sexual recombination … It is argued that the weedy habit of A. vineale is likely to have favored bulbil reproduction, {rapid population growth within habitats by asexual cloning – everyone’s a mom} whereas sexually generated genotypes may have facilitated local adaptation during the species' expansion across Europe. {a little sexual recombination increased the range of habitats invaded}

During the breeding season, one female of each mating pair mimics a male. The roles change two or three times during the season, female behavior occurring when the level of estrogen is high prior to ovulation; male behavior occurring after ovulation when the level of estrogen drops. Ovulation is more likely to occur if one individual is mounted by another; isolated lizards lay fewer eggs than those that go through the motions of sex. Apparently, these parthenogenetic lizards, which evolved from species having two sexes, till require certain sexual stimuli for maximum reproductive success. Among vertebrates, several genera of fishes, amphibians, and lizards reproduce exclusively by a complex form of parthenogenesis that involves the doubling of chromosomes after meiosis to create diploid "zygotes." About 15 species of whiptail lizards reproduce exclusively by parthenogenesis. There are no males in these species, but the lizards imitate courtship and mating behavior typical of sexual species of the same genus.

See Fig 46.13 Consider identical twins: if one dies, is it still alive? "THREE WAYS TO MAKE AN EMBRYO" Abnormal gene expression in cloned mice derived from embryonic stem cell and cumulus cell nuclei Humphreys D. et al. P NATL ACAD SCI USA 99 (20): 12889-12894 OCT 1 2002

http://aci.mta.ca/Courses/Biology/3401/The%20Final%20Reward!/Stewart-Keats/coral%20reef%20fish.htmhttp://aci.mta.ca/Courses/Biology/3401/The%20Final%20Reward!/Stewart-Keats/coral%20reef%20fish.htm Simultaneous hermaphroditism in the black hamlet {a sea bass} involves egg trading: "giving eggs to be fertilized in exchange for the opportunity to fertilize those of a partner." An hermaphrodite with ripe eggs will signal its readiness to mate. The female-role hermaphrodite will then release a small parcel of eggs to be fertilized by the male-role hermaphrodite. Male and female roles will then be reversed. {eggs are costly; sperm is cheap} As {costly} eggs are released in small parcels, and not entire clutches, only those individuals who reciprocate {by releasing costly eggs} will be allowed to {fertilize additional eggs with cheap sperm} Sexual reproduction presents a special problem for sessile animals or for parasites, such as tapeworms: encountering a member of the opposite sex. One solution to this problem is simultaneous hermaphroditism: each individual has both male and female reproductive systems. Although some hermaphrodites fertilize themselves, most must mate with another member of the same species; each animal serves as both male and female, donating and receiving sperm, as with earthworms. Each individual encountered is a potential mate.

The Caribbean bluehead wrasse is a protogynous species in which the largest (usually oldest) individuals change from female to male. These fish live in harems consisting of a single male and several females. If the male dies or is removed in experiments, the largest female in the harem changes sex and becomes the new male. Within a week, the transformed individual is producing sperm instead of eggs. http://lsvl.la.asu.edu/ubep99/abstracts/abst62/ Another remarkable reproductive pattern is sequential hermaphroditism, in which an individual reverses its sex during its lifetime. In some species, the sequential hermaphrodite is protogynous (female first), while other species are protandrous (male first). In various species of reef fishes called wrasses, sex reversal is associated with age and size.

If evolution by natural selection adapts animals to their environments, why are males & females so different? Parasitic male anglerfish Sex is a game w/ asymmetries that lead to conflicts and different optimal tactics Environment includes social env as well as ecological env. Males & females are in different social (mating) env’s. Mating systems begin with sex but differentiate around parental care.

Anisogamy notsame-size gametes The sex with the big gamete is female - by def. Females begin w/ bigger investment per gamete. Often (esp. in mammals) females continue with greater parental investment per offspring. Asymmetries in Game of Sex begin with gametes. Biased parental investment creates biased sex ratio, w/ fewer big investors available to mate at a given time (w/ females parenting, fertilizable females are scarce) If one sex has big parental investment per offspring - selection for parental effort - choosy about mating The sex w/ low parental investment per offspring -selection for mating effort -less choosy about mating

Bateman’s Principle: ‘Where one sex invests considerably more than the other, members of the latter will compete among themselves to matewith members of the former.’ Fruit flies: males females mean # offspring 0 120 0 1 2 3 # mates Note that there is stronger selection on than on to mate more than once. - eager ? - choosy ? In a diploid sexual species, in each generation, half chromosomes from males & half from females. Neither sex wins ‘battle of the sexes.’ If one male has more offspring, other males have less, because this is a is a zero-sum game within the male sex; males don’t have more offspring on average if all eggs would have been fertilized anyway, just greater variance.

Cordts R, Partridge L. 1996. Courtship reduces longevity of male Drosophila melanogaster ANIM. BEHAV. 52: 269-278. Hanging out w/ the guys p (still alive) w/ females in chastity belts Mating is costly for males. … courtship alone was sufficient to reduce male life span. Mating itself and production of seminal fluid and sperm, on the other hand, did not seem to be costly … Mounting attempts may be an indicator of an altered metabolic rate or hormonal status{stress?}that renders the males more susceptible to death.

Chapman et al. 1995. Cost of mating in Drosophila-melanogaster femalesis mediated by male accessory-gland products NATURE 373: 241-244. Mating can be costly to females too Abstract: Female Drosophila melanogaster with environmentally or genetically elevated rates of mating die younger than controls. This cost of mating is not attributable to receipt of sperm. We demonstrate here thatseminal fluid products from the main cells of the male accessory gland are responsible for the cost of mating in females, and that increasing exposure to these products increases female death rate. Main-cell products are also involved in elevating the rate of female egg-laying, in reducing female receptivity to further matings and in removing or destroying sperm of previous mates . The cost of mating to females may therefore represent a side-effect of evolutionary conflict between males {‘toxic semen!’}. { the mating game is not for good of the species!}

… in the orb-web spider N. plumipes where 60% of males do not survive copulation. … males that mate with mated females increase their fertilization success by being cannibalized. Cannibalized males generally mate for longer,but longer copulations correspond with increased paternity only in mated females. … Our data suggest that the conflict between the sexes differs between virgin and mated females. Females should always cannibalize a male, but males only gain from cannibalism when mating with mated females, not when mating with virgin females. Interestingly, the frequencies of cannibalism are not different in matings with virgin or mated females. Sexual cannibalism and sperm competition in the golden orb-web spider Nephila plumipes (Araneoidea): female and male perspectives.Schneider JM, Elgar MA. 2001. Behavioral Ecology 12:547-552. Abstract:Mating systems are frequently shaped by conflicts over reproductive interests between males and females. Sexual cannibalism can be an especially dramatic manifestation of such conflicts. Cannibalism may be in the interest of both sexes when females consume males to improve fecundity and/or males sacrifice their bodies to increase fertilization success.

Males' evolutionary responses to experimental removal of sexual selection.Pitnick et al. 2001. Proc Royal Society Of London B 268:1071-1080. Abstract:We evaluated the influence of … sexual selection upon male reproductive traits in a naturally promiscuous species, D. melanogaster. Sexual selection was removed in two replicate populations through enforced monogamous mating with random mate assignment or retained in polyandrous controls. Monogamous mating eliminates … mate competition, mate discrimination, sperm competition, cryptic female choice and, hence, sexual conflict. Levels of divergence between lines in sperm production and male fitness traits were quantified after 38-81 generations of selection. … Monogamy males evolved a smaller body size and the size of their testes and the number of sperm within the testes were disproportionately further reduced. … the fitness of monogamous males and their mates was greater when reproducing in a non-competitive context: females mated once with monogamous males produced offspring at a faster rate and produced a greater total number of surviving progeny than did females mated to control males. The results indicate that sexual selection favours the production of increased numbers of sperm in D. melanogaster and … favours some male traits conferring a direct cost to the fecundity of females.

Across primates, harem size is correlated w/ dimorphism Comparing human dimorphism (1.1) to pattern in primates suggests humans evolved dominance and mating system with at least a little polygyny Intrasexual selection for dominance & access in one sex results in sexual dimorphism within species Does size dimorphism in humans suggest anything about ancestral mating systems? Parasites as a viability cost of sexual selection in natural populations of mammals.Moore SL, Wilson K SCIENCE 297 (5589): 2015-2018 SEP 20 2002… there is a robust association between male-biased parasitism and the degree of sexual selection, as measured by mating system (monogamous or polygynous) and by the degree of size dimorphism (SSD).

More on Primate sexual dimorphism & mating system (from The Third Chimpanzee, Diamond 1992) Chimps are not size dimorphic; males do not control access to harem Increasing size dimorphism correlated with increasing male-male competition for access to copulation Humans slightly dimorphic; slightly polygynous; do guard mate(s) Gorillas are very dimorphic; males control access to harem Inverse correlation between size dimorphism vs testicle size; hyp: the more males compete for & control access to copulation, the less sperm competition Human mating system seems to have evolved w/ some competition for access to copulation and maybe a little sperm competition. Big mystery: Why human male penis so big? J. Diamond hyp: signal to other males?

Human female breasts padded w/ fat, much larger than necessary to nourish babies. Consider female choices: Angier (1999) claims male obsession w/ breasts is maladaptive Allometry of female breasts Males find ‘shapely’ breasts attractive. Hyp: Large breasts advertise, youth, health & high repro. potential.

Often animals choose mates by selecting for big signals or costly advertisements: “Status symbols” "I'm sorry Roger, but I've met someone else with brighter plumage." Status symbols signal: wealth and/or health ‘Goods’ to be delivered: good genes - indirect benefit good help - direct benefit Fitness of signaler depends on survival & reproduction The survival cost of advertising is compensated by the reproductive mating benefits

HILL GE. 1991. Plumage coloration is a sexually selected indicator of male quality. NATURE 350: 337-339 Brightened control lightened … Artificially brightened males paired more quickly and frequently than sham control or lightened males. Among unmanipulated males, plumage coloration was correlated with nest attentiveness and overwinter survival. s s Feeding visits/hr s Son’s plumage s s In addition, there was a positive correlation between the coloration of fathers and sons: “sexy sons” s dull bright In the house finch (Carpodacus mexicanus), male plumage coloration is a function of dietary intake of carotenoids. … % resighted 58  50 65 % paired 100 > 60 > 27 Days till pair 12 < 20 < 28

Burley et al. 1996. Sexual selection and extrapair fertilization in a socially monogamous passerine, the zebra finch ... Behav. Ecol. 7:218-226. female male Social vs genetic mating system: Abstract: … the percentage of young reared by a male that were not his genetic offspring … as determined … DNA fingerprinting … … were 16% and 40% for red- and green-banded males {females like red-banded males} … directly proportional to rates of female participation in unforced extrapair copulations (UEPCs) … Results suggest that … unattractive males accrue fitness gains through high parental investment (PI), ... attractive males benefit through decreased PI and increased allocation to EPF. Gill et al. 1999. Male attractiveness and differential testosterone investment in zebra finch eggs. SCIENCE 286: 126-128. … female birds deposit higher amounts of testosterone … in their eggs when mated to more attractive males {w/ red vs green leg bands} { Hunt et al. 1997. Red preference lost if filter out UV light }

Low waist-hip ratio is sexually attractive in women ... Men's physical appearance tends to communicate social dominance, which has the combined effects of intimidating reproductive rivals and attracting mates. The male beard is not obviously related to phenotypic quality ... Barber N. 1995. The evolutionary psychology of physical attractiveness: Sexual selection and human morphology. ETHOL. & SOCIOBIOL. 16: 395-424. Abstract: Psychological evidence suggests that sex differences in morphology have been modified by sexual selection so as to attract mates (intersexual selection) or intimidate rivals (intrasexual selection): Women compete with each other for high quality husbands by advertising reproductive value … by exaggerating morphological indicators ofyouthfulness such as a small nose and small feet and pale, hairless skin.

Abstract: Advertisements from 'Lonely Hearts' columns in four US newspapers are used to test hypotheses about mate preferences by male and female humans. We … confirm conventional findings that, in general, men prefer young women whose reproductive value is high while women prefer men who are slightly older than themselves ... men women Waynforth, D. & RIM Dunbar. 1995. Conditional mate choice strategies in humans - evidence from lonely hearts advertisements. Behaviour 132: 755-779.

Parental care is costly. Proximate costs: time, energy & resources Ultimate cost: reduced future reproduction Ultimate benefit: increased current reproduction What ultimately selects for parental care: The effort increases survival of current offspring (benefit) more than it decreases production of future offspring (cost) Nest desertion: a trade-off between current and future reproduction.Verboven N, Tinbergen JM 2002. ANIMAL BEHAVIOUR 63: 951-958.

Cantoni D, Brown RE. 1997. Paternal investmentand reproductive success in the California mouse,Peromyscus californicus. ANIM. BEHAV. 54: 377-386. Abstract: … single females and mated pairs of Peromyscus californicus … were required to 'forage' for food by running in a wheel. ... Females alone were able to raise litters of two pups, but not four pups. Mated pairs were able to raise a litter of four pups. … Single females that kept their pups alive had a mean inter-birth interval of 53 days; paired females had a mean inter-birth interval of 37 days. … the presence of the male resulted in four times as many pups reared over a 74-day period as a female could rear on her own. So, for male to benefit by abandoning mates to raise offspring, he would have to expect 4 times as many litters. Need for ‘babysitter/heater’ while mom forages selects paternal care.

Abstract:Pharmacological studies in prairie voles have suggested that the neuropeptides oxytocin and vasopressin {= ADH; see Fig. 45.6} play important roles in behaviors associated with monogamy, including affiliation, paternal care, and pair bonding. … Monogamous prairie voles have a higher density of oxytocin receptors the nucleus accumbens than do nonmonogamous vole species; All adaptive differences in behavior must have some underlying mechanism: Cellular mechanisms of social attachment.Young et al. 2001. Hormones and Behavior 40:133-138. blockade of these receptors by site-specific injection of antagonist in the female prairie vole prevents partner preference formation. Prairie voles also have a higher density of vasopressin receptors in the ventral pallidal area, which is the major output of the nucleus accumbens, than montane voles. Both the nucleus accumbens and ventral pallidum are key relay nuclei in the brain circuits implicated in reward, such as the mesolimbic dopamine and opioid systems. Therefore, we hypothesize that oxytocin and vasopressin may be facilitating affiliation and social attachment in monogamous species by modulating these reward pathways.

Increased affiliative response to vasopressin in mice expressing the V-1a receptor from a monogamous vole.Young LJ, Nilsen R, Waymire KG, MacGregor GR, Insel TRNATURE 400 (6746): 766-768 AUG 19 1999

Fitness depends on lifetime reproductive success: selection for individuals to invest in own offspring (or close kin) rather than unrelated offspring. 1 natural parent + 1 step parent rel risk = 40.1 Daly, M & M. Wilson. 1985. Child abuse and other risks of not living with both parents. Ethol. & Sociobiol. 6:155-176. 0 14 Victims / 1000 children in pop (1999) 1 natural parent rel risk = 12.5 2 natural parents 0-4 5-10 11-16 child’s age in years ‘Discriminative parental solicitude’ in humans? An assessment of some proposed exceptions to the phenomenon of nepotistic discrimination against stepchildren.Daly M, Wilson MANNALES ZOOLOGICI FENNICI 38 (3-4): 287-296 2001 * Note: 14/1000 = 1.4% The presence of a step-parent in the home is the most powerful statistical predictor of severe child abuse and child homicide yet discovered.

Chapter 46: ANIMAL REPRODUCTION