Adaptive explanation in socio-ecology: lessons from the Equidae

2000 ◽  
Vol 75 (1) ◽  
pp. 1-20 ◽  
Author(s):  
WAYNE L. LINKLATER
Keyword(s):  
2018 ◽  
Vol 68 (3) ◽  
pp. 227-246
Author(s):  
Nico M. van Straalen

AbstractEvolution acts through a combination of four different drivers: (1) mutation, (2) selection, (3) genetic drift, and (4) developmental constraints. There is a tendency among some biologists to frame evolution as the sole result of natural selection, and this tendency is reinforced by many popular texts. “The Naked Ape” by Desmond Morris, published 50 years ago, is no exception. In this paper I argue that evolutionary biology is much richer than natural selection alone. I illustrate this by reconstructing the evolutionary history of five different organs of the human body: foot, pelvis, scrotum, hand and brain. Factors like developmental tinkering, by-product evolution, exaptation and heterochrony are powerful forces for body-plan innovations and the appearance of such innovations in human ancestors does not always require an adaptive explanation. While Morris explained the lack of body hair in the human species by sexual selection, I argue that molecular tinkering of regulatory genes expressed in the brain, followed by positive selection for neotenic features, may have been the driving factor, with loss of body hair as a secondary consequence.


The Auk ◽  
2005 ◽  
Vol 122 (2) ◽  
pp. 509-522 ◽  
Author(s):  
Rita Hargitai ◽  
János Török ◽  
László Tóth ◽  
Gergely Hegyi ◽  
Balázs Rosivall ◽  
...  

AbstractEgg size is a particularly important life-history trait mediating maternal influences on offspring phenotype. Females can vary their egg-size investment in relation to environmental circumstances, their own breeding condition, and the quality of their mate. Here we analyzed inter- and intraclutch variation in egg size in the Collared Flycatcher (Ficedula albicollis) on the basis of eight years of data. According to our results, mean egg size increased with female condition, but did not differ among young, middle-aged, and old females. The male’s age, body size, and forehead patch size did not influence egg size; thus, we found no evidence for differential investment in egg size in relation to male quality. We found no effect of laying date on egg size when controlling for ambient temperature during the egg formation period, yet temperature had a significant effect on egg size. That result indicates proximate constraints on egg formation. Furthermore, we report on annual differences in intraclutch egg-size variation. Egg size increased within clutches in years with a warm prelaying period; whereas in years when the weather during that period was cold, there was no significant intraclutch trend. Proximate considerations seem to explain the observed patterns of intraclutch egg-size variation; however, we cannot reject the adaptive explanation. Mean egg size and intraclutch egg-size variation were unrelated to clutch size. Therefore, we found no evidence for a trade-off between size and number of eggs within a clutch.


2020 ◽  
Vol 98 (1) ◽  
pp. 73-78
Author(s):  
Hugues P. Benoît ◽  
Kadra Benhalima ◽  
Jenni L. McDermid

Senescence is the age-specific decline in fitness of adult organisms principally associated with a decline in survival rate (actuarial senescence) and fecundity (reproductive senescence). Although common in natural populations of many taxa, there are few examples in fishes. A recent study found age-specific increases in the relative frequency of macroscopically non-reproductive Atlantic herring (Clupea harengus Linnaeus, 1758), consistent with reproductive senescence in a number of Canadian populations. However, a non-adaptive explanation for these patterns, unrelated to senescence, could not be definitively ruled out. Here, we present the results of histological examination of herring gonads undertaken to examine this and another hypothesis. The sample size of macroscopically senescent gonads was small (n = 4 females), a function of the low abundance of large, older, purportedly senescent, herring in these populations subjected to high mortality rates, and constraints on obtaining fresh samples. The results indicate that these fish were senescent and not merely skip spawning, providing further evidence of senescence and the occurrence of a post-reproductive period in herring in Atlantic Canada. Based on existing theory for the evolution of senescence, observations of actuarial senescence in Norwegian spring-spawning herring suggest that this population may also experience reproductive senescence and that the phenomenon may occur broadly in the species.


2006 ◽  
Vol 57 (1) ◽  
pp. 119 ◽  
Author(s):  
R. J. Lawn ◽  
G. J. Rebetzke

The wild mungbean, Vigna radiata ssp. sublobata, is an ‘old world’ tropical species indigenous throughout the better watered areas of northern Australia. Variation among 115 accessions, mainly from Australia, West Timor, and Papua New Guinea, was evaluated for several diverse traits. The plants were cultivated in the field at 2 sowing dates, at both a tropical and a subtropical location, with 6 accessions from India and a mungbean cultivar for comparison. Substantial variation was identified for traits of potential agronomic, adaptive, or taxonomic interest. For some traits, like phenology, the variation appeared to be systematic, with plausible underlying physiological and/or adaptive explanation. Among accessions, wild type traits, like prostrate habit, more gracile morphology, twining form, and small hard seeds, tended to be associated. There was a general geographic trend for lines collected from locations more remote from where mungbean has historically been cultivated to show greater expression of wild type traits, with few ‘traits of domestication’ evident in the Australian accessions. Some of the identified variation, e.g. higher seed protein content, hardseededness, and putative disease resistance, may be of value in mungbean variety improvement. A more targetted evaluation of the collection would likely reveal other adaptations, especially tolerance to environmental stresses. As such, the wild accessions are a potentially valuable if under-utilised germplasm resource.


The Condor ◽  
2006 ◽  
Vol 108 (4) ◽  
pp. 963-965
Author(s):  
Elizabeth C. Medlin ◽  
Thomas S. Risch

Abstract Abstract Some bird species utilize snake skins as nesting material, possibly to decrease predation. We constructed 60 artificial nests simulating the nests of Great Crested Flycatchers (Myiarchus crinitus) in nest boxes to test the prediction that snake skins deter nest predators. Twenty of the boxes lacked rat snake (Elaphe obsoleta) skins (control), 20 had a single skin in the nest, and 20 had a skin in the nest and another displayed outside the box. Five of the control boxes were depredated (20%), while none of the experimental boxes were depredated. Our results supported our prediction that use of snake skins would deter mammalian predators, particularly the southern flying squirrel (Glaucomys volans). Although our results suggest a potential adaptive explanation for this behavior, our design did not allow us to address the degree of olfactory or visual detection by the squirrels, and left other potential explanations untested.


2012 ◽  
Vol 81 (2) ◽  
pp. 111-124 ◽  
Author(s):  
A. Richard Palmer

Dramatic examples of right-left asymmetry often inspire adaptive explanations, simply because it is hard to imagine how such forms could not be functionally significant. But are conspicuous morphological asymmetries necessarily adaptive? Surprisingly, in some species where direction of asymmetry is random, asymmetry in bilaterally paired traits may arise as a developmental error in a threshold trait. When cases of asymmetry are rare within a species, they are easily recognized as developmental errors. However, as asymmetrical individuals become more common, or if the asymmetry is in a signaling trait, the temptation to advance an adaptive explanation grows, particularly if the asymmetry is not clearly maladaptive. Several models of the ontogeny of asymmetry are described for both normal and anomalous random asymmetry of bilaterally paired traits. In the absence of selection, each model predicts different expected frequencies of symmetrical and asymmetrical individuals within a species, therefore such frequency distributions can effectively test for different models of development. In normal random asymmetries – where conspicuously asymmetrical individuals predominate – lateral inhibition of one side after the other has transformed appears to be an essential step in development. In anomalous random asymmetries – where conspicuously asymmetrical individuals are relatively rare – no lateral inhibition is required. Other potentially relevant variables include: purely stochastic variation in morphogen levels, useinduced asymmetry, and local (each side independent) versus central (e.g., hormonal) signaling. Examples of normal and anomalous random asymmetries are reviewed for several animal groups. A closer examination of the spectacular forelimb asymmetry in empidid dance flies raises doubts about claims that the asymmetry – both its occurrence and its direction – is adaptive, even though enlargement of the forelimbs likely is. Additional studies are required to conclude that this asymmetry is truly adaptive, as opposed to the outcome of random developmental variation in a threshold trait. This dance-fly leg asymmetry illustrates nicely how alternative hypotheses need to be considered before interpreting such variation as adaptive, even in a signaling trait.


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