Diapositiva 1

Transcript

Diapositiva 1

BIOLOGIA GENERALE
19 dicembre 2006
dispense integrate a partire da quelle della
Prof.ssa Laura Beani
Facoltà di Psicologia
Corso di Laurea in Scienze e Tecniche di
Psicologia Generale e Sperimentale
Alessandro Massolo
Dip. Biologia Animale e Genetica
c/o Prof. F. Dessì-Fulgheri (Via Romana 17)
[email protected]
Biologia generale
Massolo Alessandro
[email protected]; Tel. 347-9403330
Corso di Laurea in Scienze e
Tecniche di Psicologia Generale e Sperimentale
I SISTEMI NUZIALI
sono plastici e nascondono spesso una situazione di
PROMISCUITA’.
sono classificazioni PROBABILISTICHE: indicano che
la maggior parte della popolazione attua quella strategia
riproduttiva!
ci sono STRATEGIE ALTERNATIVE DI
ACCOPPIAMENTO intra-specie, intra-popolazione e
intra-individuo!
Modulo 3
Biologia generale
Massolo A. – [email protected]
A.A. 2006-2007
Cap 13 - L’evoluzione dei sistemi di
accoppiamento: differenze nella
distribuzione delle risorse ⇒ delle femmine ⇒
cure mono- o bi-parentali ⇒ sistemi nuziali
diversi
• Il caso degli uccelli del paradiso
• ESISTE LA MONOGAMIA?
Il dilemma dei maschi monogami: rarità delle femmine recettive + controllo
della compagna + assistenza al partner + cure parentali (10% nei
mammiferi, 90% negli uccelli) + EPC = extra-pair copulation
• Poliginia con difesa delle femmine (harem), delle risorse (territorio),
corsa competitiva (“scramble competition”), lek negli uccelli e negli
ungulati
• Poliandria e inversione dei ruoli sessuali
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Tipi di sistemi nuziali
• Monogamia
• Poligamia
– Poliginia
– Poliandria
• Promiscuità
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Monogamia
un maschio che si accoppia con una sola femmina e viceversa nella
stessa stagione riproduttiva - 1 femmina/maschio (può comparire
quando i piccoli nati richiedono la presenza di entrambi i genitori per
la loro sopravvivenza)
• Mate-assistance, mate-guarding (of male), female-enforced (keeps
others away)
• > 90% degli Uccelli – le femmine disperdono maggiormente per
raggiungere I siti con risorse migliori
• < 10% dei Mammiferi - (e.g. canidi, castoro, pipistrelli carnivori)
– I maschi aiutano a fornire nutrimento ai piccoli - canidi, marmosets
– Females solitary and males can only defend 1 female - many rodents
• C. Very rare in reptiles, amphibians, fish, insects (e.g. carrion
beetles)
(Extra Pair Copulations in birds - shows that they are not "truly"
monogamous)
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Biologia generale
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Esiste la monogamia?
Hippocampus whitei
Modulo 3
Biologia generale
Hymenocera picta
A.A. 2006-2007
Il dilemma dei maschi monogami
Nicrophorus defodiens
Modulo 3
Biologia generale
A.A. 2006-2007
La monogamia nei mammiferi
Modulo 3
Biologia generale
A.A. 2006-2007
Il valore dell’assistenza paterna
Plectrophenax nivalis
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Biologia generale
A.A. 2006-2007
DNA fingerprint
Modulo 3
Biologia generale
A.A. 2006-2007
Poligamia
sistema nuziale che coinvolge più di due partner
sessuali
• Poliginia: un maschio che feconda le uova di molte
femmine nella stessa stagione riproduttiva (Harem:
controllo diretto sulle femmine)
• Poliandria: una femmina che si accoppia con molti
maschi nella stessa stagione riproduttiva
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Biologia generale
A.A. 2006-2007
Il caso degli
uccelli del
paradiso
(Paradiseidae)
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Biologia generale
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"Le belle piume degli uccelli del paradiso sono di impaccio quando soffia il
vento” (Cap.VIII).
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Biologia generale
Paradisea di Raggi
A.A. 2006-2007
Paradisea di Raggi
Paradisea dell’Arciduca
Rodolfo
Le femmine sono
criptiche (allevano la
prole). Confrontano
possibili partner e
scelgono con chi
accoppiarsi
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Biologia generale
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Cure monoparentali
della prole
Dimorfismo sessuale variabile nei
Paradiseidi
frutti del mogano, noce
moscata: risorse ricche
e perenni
insetti:
risorsa
ricca
fichi: risorsa
effimera
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Biologia generale
Cure
biparentali
della prole
Cure
monoparentali
dellaMassolo
prole
A. – [email protected]
A.A. 2006-2007
Uccelli del paradiso
(Australia e Nuova Guinea)
1990
Dimorfismo sessuale
accentuato nelle SPECIE
POLIGINICHE (33 delle 42
che compongono la famiglia),
mentre le 9 SPECIE
MONOGAME sono
monomorfe.
Il sistema nuziale rinvia alla
STRATEGIA ALIMENTARE
(Bruce Beehler et al. : BES
1983, Emu 1987)
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Dieta specialistica (fichi):
risorsa povera di nutrienti,
a maturazione
imprevedibile. Cure
biparentali
Dieta generalista (frutti
con involucro): risorsa
ricca di proteine e lipidi,
sempre disponibile.
Cure parentali solo
femminili
Dieta insettivora, ricca
di proteine: risorsa
ricca.
Cure parentali solo
femminili
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“Le femmine rimangono più
eccitate e preferiscono maschi
più adorni, abili cantori, o che fanno
atti più buffi; ma così nello stesso
tempo scelgono i maschi più
vivaci e vigorosi.”
(Cap. VIII)
Piumaggio vistoso e parate come
effetto della scelta sessuale e
della nicchia alimentare
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S.G. Pruett-Jones, 1990 - Sexual Selection through female
choice in Parotia lawesii, a lek-mating bird of paradise (Evolution,
44)
I maschi più pronti ad esibirsi
quando arriva una femmina
(P<0.001) e con le penne
filiformi sulla testa più lunghe
(P<0.01) si assicurano un
numero più alto di
accoppiamenti.
tratti fisici e comportamentali
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Poliginia in dettaglio
•
Female defense polygyny - mammals (common) - elk, some bats, gorillas, oropendulas, some marine
amphipods
–
–
•
•
Resource defense polygyny - common in birds (example: orange-rumped honeyguide)
Males defend a resource needed by females. Resource is exchanged for matings.
Scramble competition polygyny
–
–
•
when females are grouped OR
when females have smaller territories than males
Females widely dispersed, breeding season short - 13-lined ground squirrel
Large numbers become reproductive simultaneously - horseshoe crab, wood frog
(In both cases, males with greatest success are those that move around the most)
Lek Polygyny (arena within area called a LEK)
Male doesn't defend resource, but a small territory in a display area called a LEK
E.g. Bowerbirds, manakins, some mammals (epauletted bat, some antelope)
–
Hotspot hypothesis - Males congregate where females are likely to travel, compete for best sites.
•
–
Hotshot hypothesis - Males congregate around a few very attractive males in attempt to gain matings by
association / proximity.
•
–
Example: grouse (sage and black)
Female preference hypothesis - Males congregate because females are attracted to groups of males.
•
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Example: many insects that lek
Example: kob (antelope)
A.A. 2006-2007
Lek: linguaggio venatorio, parola scandinava che significa
“gioco, esibizione”
Arena nuziale, priva di risorse, dove i maschi si
aggregano per attrarre le femmine. Compatto ⇔
Espanso.
Esibizione sincrona entro micro-territori simbolici,
possibilità di confronto e di scelta, risparmio di
tempo ed energia per le femmine.
Sistema nuziale che evolve quando le femmine si
muovono su ampi home-range che i maschi non
riescono a controllare.
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Modello hotshot (”persona di successo”): le femmine preferiscono i
maschi più attraenti, gli altri prendono posto intorno.
Arene che si spostano intorno ai maschi più attraenti nel gallo
forcello.
Tetrao tetrix
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Modello hotspot (“punto
caldo”): le arene si trovano
nei punti di passaggio
delle femmine.
Kobus leche kafuensis
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Guardia sulla compagna
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Poliginia selettiva
Parus caeruleus
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Poliginia con difesa delle femmine
maschio
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Massolo
Phyllostomus
hastatus
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Poliginia con difesa delle femmine
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Poliginia con difesa delle risorse
Lamprologus callipterus
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Poligamia o monogamia?
Marmota flaviventris
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Poligamia maschile e successo riproduttivo
femminile
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Biologia generale
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Poligamia nella corsa competitiva
Citellus tredecimlineatus
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Poligamia nella corsa competitiva e
apprendimento dei maschi
Citellus tredecimlineatus
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Biologia generale
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Poligamia nella corsa competitiva: i
limuli
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Poligamia nei lek
Manacus manacus
trinitatis
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Biologia generale
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Poligamia nei lek
Epomophorus monstruosus
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Poligamia nei lek: maschi attraenti
Tetrao tetrix
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Poligamia nei
lek: preferenza
delle femmine
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Biologia generale
Kobu leche kafuensis
A.A. 2006-2007
Poligamia nei lek punti caldi
Kobus kob
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Poligamia nei lek:
maschi attraenti e punti caldi
Philomanchus pugnax
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Biologia generale
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Variazioni del sistema di accoppiamento nella
passera scopaiola
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Sollecitazioni all’accoppiamento
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Poliandria
• Poliandria: una femmina che si accoppia con molti maschi
nella stessa stagione riproduttiva
– Maggiore variabilità nella morfologia degli spermi, maggiori
vantaggi materiali, maggiori cure parentali da parte dei maschi
– Rara negli uccelli, molto rara nei mammmiferi, comune nei pesci
– Compare negli uccelli, quando le risorse sono frammentate e
disponibili solo per brevi periodi di tempo
• Sequenziale - sanderling, spotted sandpiper (piccoli precoci, maschi extra)
• Simultanea - jacana, phalarope (difende I maschi da altre femmine)
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Sanderling
Spotted sand piper Actitis macularia
Jacana jacana
(Falaropo beccosottile (Phalaropus lobatus)
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Poliandria
Cordyluchernes scorpioides
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Poliandria e benefici
materiali
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Poliandria con
difesa delle risorse
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ActitisMassolo
macularia
A.A. 2006-2007
Poliandria con difesa del compagno
Phalaropus lobatus
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Promiscuità
• Entrambi i sessi si accoppiano più volte con +
partner
– Comune negli insetti
– E’ presente in alcuni mammiferi (p.es. pipistrelli), pesci
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CONFLICTS BETWEEN THE SEXES CAN LEAD TO A
DIVERSITY OF MATING SYSTEMS
Polygynandry (not promiscuity)
Example: Dunnock
– A. Dunnocks may show monogamy, polygyny, polyandry, and polygynandry
– B. Cloaca pecking precedes copulation
• Ejection of sperm from previous matings
• Frequent interruption by (esp. alpha) males
– C. Reproductive success in different systems depends on environmental quality
• Males usually do better with polygyny, but may do better with polyandry if environmental
quality is poor (less conflict in that case)
• Females do better with polyandry, but difference greatest in poor environment
Alternative Breeding Strategies
– A. Previous examples:
• Different types of males (Isopods)
• Satellite males (toads) - "sneakers" - American toad microclimate ex.
– B. Changing sex: fish
• Blue-headed wrasse - protogynous
• Anemone fish - protandrous
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I sistemi nuziali nei primati
• Monogamia nei primati: ca 14% delle specie.
• Gibboni monogami
– Both males and females are the same size.
• Gorilla poligami
– the males dominate harems of several mature females
– males are much larger, often by a factor of 2, than
females (in technical terms, they are 'sexually
dimorphic').
• Uomo?
– humans are much less dimorphic than gorillas, markedly
more than gibbons, and a little bit less than
chimpanzees.
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Homo sapiens?
Maschi 170-175; Femmine 158-163
Ratio 1,043-1,10 (1,075)
8,90 femmine/maschio
1,75 femmine/maschio
Relationship between degree of polygyny (mean harem size) & sexual dimorphism in primates (from Barash 1982; based on data from Alexander et al. 1979).
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Related to this are further differences in body structures that go beyond sheer size.
• First, with respect to males, Short (1979) noticed that whereas male gorillas are four times
the weight of male chimpanzees, a chimpanzee's testicles are four times the weight of
those of the gorilla!
– In addition, the mating activities of the two species are quite different.
•
•
Gorillas mate at a leisurely pace:
a chimpanzee male can perform in six seconds, from start to finish, and they do this in the presence of a
large number of other males.
– But, as with gorillas, chimpanzees are under the sociobiological 'rule' to attempt to maximise their
chances of getting their complement of genes through to the next generation.
– select males not for increasing body size, but for increasing testicle size.
not all sperm are produced for purely reproductive purposes, but might have other functions:
chimpanzee males would benefit if they produced kamikaze sperm, whose function was to
seek out and destroy the reproductive sperm of other males that was present in the female.
You get the idea quite clearly from the title of a recent paper in Nature by Pizzari and
Birkhead (2000): Female feral fowl eject sperm of subdominant males.
•
Gorilla females show small bodily changes when they ovulate; female chimpanzees
show a very large sexual swelling (and human females show almost none, a situation
termed 'concealed ovulation').
– In the case of the chimpanzee, her period of ovulation is a very publicly advertised event, and she
attracts a large number of males around her. In addition, she is promiscuous, and ready to mate
with almost any male, and often one after another, and in public.
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La femmina si accoppia:
Con più maschi
Con un maschio
Scelta femminile e forme dei peni
nei primati: stimolazione più
intensa (e ritenzione dello
sperma) se le femmine si
accoppiano con più maschi?
(“cryptic female choice”, Eberhard)
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Sistemi nuziali nell’uomo
Bigamy is having one wife too many. Monogamy is the same.
Oscar Wilde
Woman wants monogamy
Man delights in novelty
Love is woman's moon and sun
Man has other forms of fun
Woman lives but in her lord
Count to ten and man is bored
With this the gist and sum of it
What earthly good can come of it?
Dorothy Parker
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EEA - Environment of Evolutionary
Adaptation
• Thus, the claim is that we can expect that humans
would have evolved to be in tune with the
requirements of this form of life, rather than the
agricultural or industrial societies that have been
elaborated more recently.
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Differenze sessuali nella tattiche di accoppiamento
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Differenze di selettività
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Sistemi nuziali nell’uomo
ca 19% delle società umane sono strettamente monogame, ma
La maggior parte dei matrimoni sono monogami anche se la maggior parte delle
società permette la poliginia.
La poliandria è rara nei mammiferi e nei primati (anche nell’uomo).
60%
50%
40%
30%
20%
10%
0%
Polyandry-primarily
monogamous
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Monogamy
Polygyny < 20% plural
wives
Polygyny >20% plural
wives
Figure 1. Frequency of Marriage Types Across Cultures
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Cultura e sistema nuziale
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Preventing infanticide
•
At the same time as Short published his musings on ape genitalia, Sarah Hrdy (e.g., 1979)
published her studies of langur monkeys in Rajasthan. Whereas one might expect that
females would be choosy about whom they picked to sire the offspring that they would carry
through pregnancy and invest so much parental care in, Hrdy found that
– female langur monkeys mate indiscriminately with the males. Hrdy argued that there was
something wrong with our expectation, not with the females.
•
•
female monkeys and apes adopt particular strategies of mating behaviour - the details of
which vary depending on the nature of the food supplies they rely on to rear their young
and sustain themselves through the vicissitudes of motherhood - in order to lessen the
chances of males killing their infants. Hence, in some circumstances, it could be a 'good
thing' to have the protection of a dominant male who would deter any attacks on her infant.
In other circumstances, it could be a good thing if no male in the group had any knowledge
of an infant's paternity, since this would deter each male from attacking any infant, since he
could be its father.
humans?
– Daly and Wilson (1988) reviewed much of the relevant data, and found that stepchildren are 65
times more likely to die than children living with their natural parents.
– That is, in preventing potential infanticide, the female either has to act to ensure that the child's
father is sure he is the father, so that he will protect the infant from threats from other men;
or she has to have acted so that the male has been subject to selection that increases his
chances of being the father of any children around, particularly hers.
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What are men for?
“Women need men like fish need a bicycle”
• increasingly large brains that human ancestors were going
in for, something had to give: you just can't get big heads
out through small pelvic openings.
– human infants are much more helpless, and for longer, than the
infants of other primates.
• Men are useful things to have around
• First, women need men so as to provide them and their infants with
protection from predators and with food.
• Second, it's in a man's interest to provide that protection, providing he
knows it is his infant.
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Sistemi nuziali?
•
births tend to be spaced 4 years apart. This is about the time that:
–
–
–
•
infants have become sufficiently autonomous to allow the mother to attempt to cope with a second child's
demands;
the rigours of pregnancy and child-rearing have decreased enough to allow her to build up body fat to the
level needed to recommence ovulation; and
infants are weaned in these societies, reducing lactation, and lifting the repression of the ovulatory cycle that
lactation creates.
Now, in addition, Fisher (1992) has looked at the data for present day 'divorce' across a range of
cultures and societies. What she found was that
–
–
–
–
the breakdown in human 'marriages' peaks at four years.
The conclusion she draws is that, given how vastly different cultural practices and value systems are, with
different beliefs about the mechanics of marriage and the like, finding any pattern at all is unlikely, but to get one
that points to a period of time that fits with the 'natural' reproductive patterns is quite remarkable.
Her claim is that humans have been selected to organise their parental relations along a system of serial
monogamy. And in addition, divorce peaks occur for women between 20 and 29 years of age, and for men
around 25 to 29 years of age, which tend to be respectively the ages of their highest fertility. This would be a
peculiar time for a male to leave a female, all other things being equal.
But it would give both parents a chance of trying out a different combination of genes for their second child,
provided they have survived the rigours of raising the first one.
Well, maybe. But let's go down another route again for a while.
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Evolutionary pressures
• Baker and Bellis (1989) asked some pretty basic
questions about what happens in human sexual
reproduction.
– If when making love a woman has no orgasm, or has one
more than a minute before the man ejaculates, then very little of
his sperm remains in her vagina.
– If her orgasm was less than one minute before or up to 45
minutes later than his ejaculation, then most of his sperm stays
in.
– In addition, the longer it was since she had previously had an
orgasm, then the more sperm she retains.
– Finally, the amount the man ejaculated related to whether the
couple had been together during the day or apart. If they had
been together, the amount was less than if they had been apart.
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Competizione spermatica nell’uomo
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Women choice
• Baker and Bellis also asked the couples in their study about their
extramarital affairs.
– In faithful women, about 55% of orgasms were high sperm retention.
– In unfaithful women, 40% were with their regular partner, but 70% were with
their lover.
– In addition, the extramarital intercourse generally occurred at the woman's
most fertile period. The result is that a woman in their study could have
intercourse twice as often with her partner as with her lover, but still be more
likely to conceive a child by her lover.
• They subsequently found, via genetic testing, that for two populations
in northern and southern England, fewer than 4 in 5 (<80%) children
were the offspring of their ostensible fathers.
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Monogamy
we would appear to be 'designed for a system of monogamy plagued
by adultery' Ridley, 1994: 170). The likely strategies that would be
favoured if male and female reproductive behaviour were to have any
genetically-transmitted base would be:
– 1. Differential investment results in males initiating courtship, and females
choosing.
– 2. Males tending to short-term relationships; females tending to long-term
relationships.
The kinds of points used in substantiation of these claims are:
• The supposed hunter-gathering way of life (termed by one
anthropologist 'the original affluent society') characteristic of our EEA
does not lend itself to polygamy since
– luck plays a major part in hunting, and affects the returns of even the best
hunter. Meat cannot be stored, so there is little chance to accumulate 'wealth',
and thus no man has much more in the way of resources than any other.
Monogamy is the tendency in such situations.
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Polyandry
•
There is only one truly polyandrous society, in
Tibet (Crook and Crook, 1988), and here the
ecological conditions under which people are living
are highly unusual, and this form of organisation
appears to be regarded as a temporary
arrangement even by its own members, existing
only until they have the resources to seek individual
partners.
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Polyginy
Adopting an agricultural way of life
Simple agricultural societies often see harems of up to 100 women per man (Cashdan, 1980).
Betzig (1986) to the view that people are sexually motivated to exploit whatever situation they encounter to their best ends within the
constraints of a set of tactics, seemingly different for men and for women, that became part of our innate strategies during the period in
which we evolved.
Hence, men have been selected to form coalitions that enable them to gain power in a group, in the first place, and later to use that power
to accumulate wealth.
Power and wealth interact to influence the evolutionary process by indirect action - men use their brains rather than brute force to forge
coalitions to win power. This breaks the link between bodily strength and power over resources (this break being aided massively by
'weapon technology'), and leads to the restrained sexual dimorphism we humans show.
Thus Betzig hypothesises that men will treat power not as an end in itself, but as a means to sexual and reproductive success. The
evidence is in line with this prediction. For example, she found that, for 104 societies, 'in almost every case, power predicts the size of a
man's harem' (Betzig, 1986).
•
Women are attracted by men with power, as power means to secure resources and protection for their children.
But they do this within the constraints of a psychological make-up that was evolved in conditions that favoured monogamy. Hence:
–
–
–
•
???
–
–
–
•
1. Women most commonly seek a monogamous marriage, even in polygamous societies.
2. Women do not as a rule seek promiscuous variety per se.
3. Women are sometimes unfaithful.
a. Blame men for being marvellous seducers. That is, there is no inherent tendency for women to act in this way.
b. Blame the stresses of modern life that lead to unhappy marriages, lack of personal fulfilment, etc. That is, the activity is a consequence of modern life, and of
no consequence in an evolutionary sense.
c. Or..? There are advantages to both sexes within a monogamous marriage system in seeking alternative sexual partners, in that this enables males to have
more young, and enables females to have better young.
for most women, monogamy provides a resource to assist in childrearing. But their 'husband' may not be the best 'mate'.
Modulo 3
Biologia generale
A.A. 2006-2007
Controllo della compagna
Modulo 3
Biologia generale
A.A. 2006-2007
References
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Baker, R.R. and Bellis, M.A. (1989) Number of sperm in human ejaculates varies in accordance with
sperm competition. Animal Behaviour 33: 867-9.
Betzig, L. (1986) Despotism and differential reproduction: A Darwinian view of reproduction. New York:
Aldine.
Cashdan, E. (1980) Egalitarianism among hunters anf gatherers. American Anthropologist 82: 116-20.
Crook, J.H. and Crook, S.J. (1988) Tibetan polyandry: Problems of adaptation and fitness. In L. Betzig et
al. (eds) Human Reproductive Behaviour. Cambridge: Cambridge University Press.
Daly, M. and Wilson, M. (1988) Homicide. New York: Aldine.
Fisher, H.E. (1992) The anatomy of love: The natural history of monogamy, adultery and divorce. New
York: Norton.
Hartung, J. (1982) Polygyny and the inheritance of wealth. Current Anthropology 23: 1-12.
Hrdy, S.B. (1979) Infanticide among animals: A review, classification and examination of the implications
for the reproductive strategies of females. Ethology and Sociobiology 1: 13-40.
Portmann, A. (1941) Die Tragzeiten der Primaten und die Dauer der Schwangerschaft beim Menschen:
ein Problem der vergleichen Biologie. Revue Suisse de Zoologie 48: 511-18.
Ridley, M. (1994) The red queen: Sex and the evolution of human nature. London: Penguin.
Short, R.V. (1979) Sexual selection and its component parts, somatic and genital selection, as illustrated
by man and the great apes. Advances in the Study of Behaviour 9: 131-58.
Modulo 3
Biologia generale
A.A. 2006-2007

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