Acoustic MimicryBiology 342 Fall 08Marion Burrill and Shreya Shrestha |
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PhylogenyPhylogeny, from the Greek phyle = tribe, race and genesis = birth, refers to the evolutionary relationships between organisms. The phylogeny of a specific organism refers to its evolutionary history or lineage. Phylogenies can be reconstructed in a variety of ways. Some are based on molecular similarities between groups of organisms, others are based on morphological comparisons gleaned from the fossil record, and still others use combinations of the both approaches. It is often interesting to know whether a specific trait has arisen multiple times in organisms that are distantly related or whether they have arisen only once and all organism with that trait are descendent form a common ancestor. Flowchart demonstrating the evolution of different sectors in the bat-moth predator-prey paradigm involving acoustic mimicry (each have been explained in the text below)
Evolution of mimicryIn a complex system where multiple prey species are available, there is an intense selection on unprofitable prey to mimic each other (Beatty et al., 2004). The primary selective force is acquired learning in predators enabling them to better distinguish between profitable and unprofitable preys based on the distinct phenotypes of the latter (Beatty et al., 2004; MacDougall and Dawkins, 1998; Ruxton, 1998). Unlike Muller’s suggestion, predators do not completely rely on associative learning while foraging but rather use simple rules for discriminating between profitable and unprofitable preys (Beatty et al, 2004). Mullerian mimicry is more likely to arise in a multispecies community such as that observed in the bat-moth interaction paradigm. There have been conflicting theories posited on the evolution of mimicry as being sudden versus gradual (Rettenmeyer, 1970). One side of the argument propounds that for effective protection against predators, organisms must evolve mimicry via major mutations or saltations as envisioned by Goldschmidt (1945 and 1952). On the other side, it has been demonstrated using mimic-model pairs that mimetic evolution is a gradual process, an accumulation of small steps over a period of time. Fisher argued in 1958 that a mimic arising from a macromutation in a switch gene would be comparable of females arising from males since sex is determined by a single chromosome or a few genes. It is more plausible that mimics in a predator-prey paradigm like ours arose from gradual evolution over a long period of time under the predator-induced selective pressures. Selection for or against aposematic strategies like acoustic mimicry is susceptible to variation in predator and prey that engender variation in profitability among species and individuals. The net profitability of preys will vary in the lifetime of an individual predator which can be attributed to the relative abundance of other preys, fluctuation in the nutritional value of the prey, efficacy of its defense mechanism, etc. Aposematism in general and acoustic mimicry in particular can be affected by variations in selection induced by microgeographical and geographical factors (Mappes et al, 2005):
The origin, spread, and maintenance or the evolution of aposematism is a therefore a function of variations in space and time. In a good year or in a high-quality territory teeming with prey fauna, the predator might be highly selective, avoiding even the weakly aposematic preys which would enable the initial spread and further strengthening of aposematism in these prey populations. We would expect these new forms or weakly aposematic preys to be a developmentally plastic population whose aposematism would get entrenched in the population by genetic accommodation (West-Eberhard, 2005) and further enhanced given the maintenance of stable conditions of avoidance by the predator. An intermediate season/territory would select for the existing aposematism but not support novel, burgeoning ones still in their weak primitive stages. In low-quality territories or in a bad year, aposematism will be selected against since starving predators wouldn’t discriminate between aposematic and alternate preys unless aposematism has evolved for so long in these territories that it has developed to incorporate emetic or predator-weakening effects.
Evolution of echolocation in bats
Molecular tree of existing bat families constituting of two clades: Yinpterochiroptera and Yangochiroptera. The latter clade consititutes of all echolocating bats while the former clade includes the non-echolocating (except by tongue-clicking in one genus) superfamily Pteropodidea with the echolocating superfamily Rhinolophoidea. Colored boxes, branches and names represent the six superfamilial groupings shown. (Jones and Teeling, 2006)Evolution of moth ear
Evolution of tymbal:
Evolution of toxicity
Sequential demonstration of approach and capture of a non-toxic moth (Galleria mellonella) by a big brown bat (Eptesicus fuscus); the sequence delineates multiple points where the decision to reject the prey (if unprofitable) can be made. (Hristov and Connor, 2005)
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