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Week 12 BIOC54.docx

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Department
Biological Sciences
Course Code
BIOC54H3
Professor
Kamini Persaud

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Description
Week 12: Communication Learning; CH 9 pg 287 – 294 & 299 – 326, CH3 pg 97 -104 Pg 287 – 294 The Origin and Modification of a Signal Spotted hyenas and their “pseudo penis” – looking at 4 different species of hyenas and their behaviour – engage in chemical communication (use of anal glands to mark habitats) & they also inspect the anogenital regions of their companions. L.Harrison Matthews proposed that the pseudopenis was a result of high levels of male sex hormones in female hyenas. Gould introduced this hypothesis by stating that the penis and clitoris are both made from the same embryonic tissue and become what they are based on the exposure to certain hormones (testosterone and androgen = penis, absence of androgens = clitoris). However, when a female embryo comes into contact with androgens, experimentally or naturally, she develops an elongated clitoris that resembles a penis. According to a paper written by Racey & Skinner, female spotted hyenas had circulating levels of testosterone equal to that of males. Some other experiments were done testing the levels of testosterone in females and males and found that females had less testosterone then males although it did become about the same when the female was pregnant. Since the mothers placenta converts androstenedione to testosterone it could be exposing the female embryo to male hormones, however there are other hormones that target to inactivate these male hormones when the embryo is female. Another experiment done was to inject a pregnant female with anti-androgenic chemicals to prevent the androgens from creating a pseudo penis is females, however even with them, the females still had pseudo penis albeit a bit smaller. The only other explanation is to suggest that mutation was the governing result of the pseudo penis in female hyenas and that the mutation served to either lower male-like androgen concentrations present in ancestral females or modified their effects, thereby reducing the damaging developmental by-products of exposure to androgens for females. The Adaptive Value of a Signal Why are male-like characteristics in females (pseudopenis) preferred over those females that do not, especially when females can become sterile when exposed to male hormones, when 10% of them die after their first child birth, and about 60% of all hyena cubs die as well. Proximate cause - a # of by-product hypotheses for the trait. One being that increased androgen levels in females spread since it helped make adult females larger and more aggressive, not because of acquiring a pseudopenis. More androgen exposure does lead to a more aggressive female in comparison to males. Females also keep a hierarchical system for their own sex, which gain them priority to the meat of the kill, and also must keep males in their place. Top females are able to hunt within the clan, which lead them to be more successful, reproductively speaking, while subordinate females must hunt outside the clan which can be risky. Top females also produce more androgens during the second half of pregnancy, allowing these benefits to be passed on to their cubs. The first hypothesis proposed (social-bonding) for the adaptive trait of the pseudopenis was that an erect pseudopenis aids in reducing tension among the highly aggressive female members of a clan, promoting social bonds that kept the group together to work for the mutual benefit of all. A second hypothesis proposed (sexual mimicry) was that the pseudopenis allows for some mimicry of males by females in order to divert aggression away from them, since females are tricked into treating an individual with a pseudopenis as if she were male. Problems with this hypothesis include the assumption that hyenas identify males and females by visual cue when really they rely on olfactory and auditory cues. An Adaptationist Hypothesis Historically a male’s erect penis would signal to the female that he is non-threatening and would encourage the female to accept him as a mate rather than reject. Females would be able to use their pseudopenis in the same regards, as to signal subordination to a mate while also establishing a strict dominance hierarchy among females. Also, the pseudopenis poses and advantage to low ranking females who can signal their subordination to other females to stay in the clan rather than being casted out. Social harmony is displayed in this theory from the subordinate’s acceptance of its status relative to a more dominant individual. Social mimicry is displayed in this theory to the extent that females behave like males to demonstrate their rank relative to other females and not to deceive their companions about their actual sex. p299 - 326 Sensory Exploitation of Signal Receivers Male whistling moths use ultrasound to communicate since an ancestor of theirs had bat predators which made ultrasounds more reproductively advantageous. Relating this to the pseudopenis of female hyenas, it is easier to understand the function of something new when it has played a role before in the past, like the whistling moths. In one group of bowerbirds, males use a harsh and raspy “skraa” call when courting females, which was almost certainly used for male-male aggressive signals. This co-opt of signals has made it advantageous for females to make and adaptive choice about mates. Sensory Exploitation – using a novel signal to tap into pre-existing perceptual mechanism in a signal receiver. Ex. Courtship of male water mites, which “exploit” the predatory behaviour of females waiting to ambush their prey (copepods). When the predatory female is in her attack position (called “net stance”) the male will vibrate a foreleg in front of her, then she grabs him, let’s go (not harming the male) and the male places spermatophores near the female. If she is receptive, she will pick them up in her genital opening. It is not a perfect theory since one suggestion is that more hungry females may be more willing to attack and mate just to gain the nutrient-rich spermatophore. Ex. Male and female guppies – male guppies are especially attractive to females when they have bright orange spots on their skin which they can only express when eating a certain plant that is rich in carotenoids. A hypothesis for why females find this so attractive is based on a by-product of a sensory preference that had evolved in another context. Female guppies would occasionally feed on orange fruits that would fall in the stream where they lived, so females could have gained a sensory bias to the colour orange because of a foraging benefit associated with the ability (orange skin). Females do tend to approach the orange disc more often and actually try to bite them. Experiments were done across many species that altered their natural attributes to those that could not be produced naturally (extremely artificial). In all cases females preferred the artificially enhanced male rather than the natural one. Another explanation for this bias is that an ancestor in the past may have used these attributes to assess a mate, and the species now still have that existing bias even though mates cannot grow such attributes. Ex. Lizard Sceloporus virgatus, which lack the large blue abdominal patches of many other members of its genus. The blue patches were used in male threat posture, althought the display is still not lost. When painted blue patches on the male, and they did their display, other males would back off more readily whereas with no paint this was not the case. Another hypothesis – are there signal receivers that have a preference for signals that neither they nor their ancestors ever possessed or responded to? One way to test is to attribute a species with a trait that would have not been in their ancestral past. Burley and Symanski outfitted zebra finches and long-tailed finches with ridiculous white feathers glued to their head. Even though this trait has never been seen now and in the past, females associated more with the male finch with the novel trait as opposed to the other males. Some arguments against the sensory bias hypothesis for female preference in swordtails (covered in lecture) have to do with a detailed phylogeny of the xiphophorus that swords have evolved and been lost several times in this genus of fish. Sexual display traits are likely to change rapidly over evolutionary time, which could make it difficult to reconstruct evolutionary history via the standard comparative approach. Also some researches also express that an arbitrary preference such as an elongated tail could actually just be an adaptive preference for a more general trait, such as a large body. However at the ultimate level of things females can benefit for going after these males that can exploit their pre-existing sensory bias since they can gain sons that can inherit the trait or a male with exaggerated courtship signals were physiologically capable of helping to rear a choosy female’s offspring. If evolution favoured females who developed a resistance to such exploitation displays that we would see a change towards females who do not select for such traits. However it can be costly to females to do so under some circumstances. Ex. Is in the female garter snakes. They open their cloaca in order to deter predators away using the odorous chemicals and feces released from an open cloaca. However males copulate with females by inserting their intromittent organ into the cloaca. Even though females subject themselves to males when opening their cloaca they also deter predators which if they didn’t they would probably die. Adaptionist Questions about Communication Darwinian puzzles in communication appear when observers see signal gives or receivers apparently disadvantaged by their actions. If giving or receiving a signal lowers fitness, then the behaviour for it should disappear over time. Heinrich started studying ravens when he heard one raven call out to others while feasting on the carcass of a moose. The puzzle here was, why attract competition to your food source instead of reaping all of the benefits (the food) for yourself. One theory was that the raven was calling other ravens within its family (relatives) but according to DNA fingerprinting they were all unrelated. Another hypothesis was that the call would attract a type of carnivore (wolf or bear for example) to open up the carcass so the ravens could get to the inside easier and feast. Exp. Wave a goat carcass by day to attract a raven and observe the behaviour. Results: ravens did not call out/yell when carcass was not open, but they did when it was open, which proves the hypothesis wrong. His other hypothesis was that the raven was attracting other ravens in order to decrease its chance of being attacked by a hiding predator (coyote or fox). However, even after acquiring a group of other ravens for security, the raven still was calling out and yelling, which also fails as a hypothesis. While still carrying out the goat experiment, he then observed that the calling only happened when 3 or more ravens had arrived at the carcass location (did not happen with 2 or less). Since ravens tend to form pairs on certain territories, the pair would often challenge the intruder for the carcass and try to drive them off their territory. Because of this he hypothesized that the intruder raven would call out in order to gain protection from the resident pair, in order for the intruder to feast instead of being kicked out. The “gang up on the territorial residents” hypothesis leads to a number of predictions: 1) resident territory owners should never yell, 2) non-resident ravens should yell, 3) yelling should facilitate a mass assault on a carcass by non-resident ravens, 4) resident pairs should be unable to repel a communal assault on their resources, and 5) a food bonanza (resource) should be eaten by either a pair alone or by a mob of ravens. He found that all these predictions were true and conclude that yelling, although brings a cost of sharing the food, it also brings the benefit of feasting and also not getting attacked by resident ravens. Why Do Baby Birds Beg So Loudly? Comparing the begging approach of some baby birds to others, the ones that beg the loudest attracted the most amount of predators and were eaten/or eggs were ta
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