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Sherratt TN 《Die Naturwissenschaften》2008,95(8):681-695
It is now 130 years since Fritz Müller proposed an evolutionary explanation for the close similarity of co-existing unpalatable prey species, a phenomenon now known as Müllerian mimicry. Müller's hypothesis was that unpalatable species evolve a similar appearance to reduce the mortality involved in training predators to avoid them, and he backed up his arguments with a mathematical model in which predators attack a fixed number (n) of each distinct unpalatable type in a given season before avoiding them. Here, I review what has since been discovered about Müllerian mimicry and consider in particular its relationship to other forms of mimicry. Müller's specific model of associative learning involving a "fixed n" in a given season has not been supported, and several experiments now suggest that two distinct unpalatable prey types may be just as easy to learn to avoid as one. Nevertheless, Müller's general insight that novel unpalatable forms have higher mortality than common unpalatable forms as a result of predation has been well supported by field experiments. From its inception, there has been a heated debate over the nature of the relationship between Müllerian co-mimics that differ in their level of defence. There is now a growing awareness that this relationship can be mediated by many factors, including synergistic effects between co-mimics that differ in their mode of defence, rates of generalisation among warning signals and concomitant changes in prey density as mimicry evolves. I highlight areas for future enquiry, including the possibility of Müllerian mimicry systems based on profitability rather than unprofitability and the co-evolution of defence. 相似文献
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We investigated the benefits of larval cannibalism in the Neotropical mosquito Trichoprosopon digitatum. The clutch size of the mosquito in the field was strongly correlated with adult female size, indicating a fitness advantage
to being large. In controlled laboratory experiments, we compared the survivorship and eventual adult sizes of larvae that
were given the opportunity to cannibalise conspecifics throughout their lifetimes with the survivorship and adult sizes of
larvae that were prevented from cannibalising. Since the benefits of cannibalism are likely to depend on the context in which
it occurs, the experiment was conducted at two levels of alternative food availability. When food availability was high most
larvae survived to adulthood, females cannibalised more than males and there was no measurable advantage to cannibalism in
terms of survival rate, emergence time or adult size. Larvae were significantly more cannibalistic when food availability
was lower, although under these conditions no larvae survived to adulthood. Nevertheless, under low food an important fitness
benefit to cannibalism was revealed: individuals which had the opportunity to cannibalise survived significantly longer as
larvae than those which did not. This increased longevity is likely to provide an important advantage to mosquito larvae when
they wait for the input of unpredictable food sources.
Received: 7 October 1995/Accepted after revision: 13 April 1996 相似文献
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Sue?LewisEmail author Keith?C.?Hamer Luisa?Money Richard?Griffiths Sarah?Wanless Thomas?N.?Sherratt 《Behavioral ecology and sociobiology》2004,56(1):81-88
Among species where there is a risk to leaving offspring unattended, parents usually take alternating shifts guarding their young. However, they may occasionally exhibit brood neglect by leaving their offspring unattended at the nest. To investigate this phenomenon further, we examined the foraging behavior of the northern gannet (Morus bassanus) during chick-rearing. This species has a prolonged nestling period (13 weeks) and the single chick is usually guarded by one or other of its parents, because unattended chicks are frequently attacked by conspecifics. We tested the prediction that the foraging behavior of adults when they left their offspring alone at the nest (unattended trips) would differ in character to when adults left offspring with their partner (attended trips). Brood neglect typically occurred after a longer-than-average attendance period at the nest. Unattended trips were, on average, about half the duration of attended trips, and therefore much closer to the colony. There was also a difference in departure direction between attended and unattended trips, with unattended trips tending to be northeast of the colony. Chicks were fed by parents after both attended and unattended trips, but the frequency and the duration of unattended trips increased as chicks grew older whereas the duration of attended trips decreased as chicks grew. These results indicate that parents may be making a trade-off between risk of attack to their offspring and food-intake rate, and that the solution to this trade-off is dependent on chick age.Communicated by C. Brown 相似文献
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Effects of extreme variation in female morph frequencies on the mating behaviour of male damselflies
Janice J. Ting Jessica Bots Felipe Pérez Jvostov Hans van Gossum Thomas N. Sherratt 《Behavioral ecology and sociobiology》2009,64(2):225-236
Female-limited polymorphism is often attributed to selection to avoid excessive male mating attempts. It is encountered in
various taxonomic groups, but is particularly common in damselflies, where one female morph (andromorph) typically resembles
the conspecific male in colour pattern, while the other(s) (gynomorph(s)) do not. Two sets of theories have been proposed
to explain the phenomenon in damselflies, which can be classified as the learned mate recognition (LMR) and male mimicry (MM)
hypotheses. To test predictions of these hypotheses, we evaluated the rate of male sexual response towards female morphs and
conspecific males in the damselfly Nehalennia irene. The LMR hypothesis predicts that males should respond sexually to andromorphs at greater rates in populations containing
a higher relative frequency of andromorphs. The MM hypothesis predicts that males respond more often sexually to both andromorphs
and males as the ratio of andromorphs to males increases. While LMR predicts that the rate of mating attempts towards gynomorphs
should vary, the MM predicts that it should be relatively fixed. On experimentally presenting live specimens to focal males
in five different populations with extreme variation in female morph frequencies, we observed that as the andromorph frequency
and ratio of andromorphs to males increased, the proportion of male mating attempts increased on both andromorphs and males,
whereas it decreased on gynomorphs. While the simplest form of the MM hypothesis is rejected, the results support specific
predictions of both hypotheses and suggest that future studies should not treat these hypotheses as mutually exclusive. 相似文献
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