The Role of Analogy in Adaptive Explanation

<p>Cases of 'convergence' (traits which have independently evolved in two or more lineages) could play an important role in the construction and corroboration of adaptive hypotheses. In particular, they could inform us about the evolutionary histories of novel traits. However, there is a problem of causal depth in the use of analogies. Natural Selection's affect on phenotype is constrained by phylogenetic history to a degree that we are unfounded in projecting adaptive stories from one lineage to another. I will argue for two approaches to resolve this issue. First, by constraining our catchment area to closely related lineages we can control for developmental noise. Second, by integrating analogies into explanations which incorporate other streams of evidence or bootstrapping an analogous model across many instantiations, we can overcome the problem of causal depth.</p>

The Role of Analogy in Adaptive Explanation

<p>Cases of 'convergence' (traits which have independently evolved in two or more lineages) could play an important role in the construction and corroboration of adaptive hypotheses. In particular, they could inform us about the evolutionary histories of novel traits. However, there is a problem of causal depth in the use of analogies. Natural Selection's affect on phenotype is constrained by phylogenetic history to a degree that we are unfounded in projecting adaptive stories from one lineage to another. I will argue for two approaches to resolve this issue. First, by constraining our catchment area to closely related lineages we can control for developmental noise. Second, by integrating analogies into explanations which incorporate other streams of evidence or bootstrapping an analogous model across many instantiations, we can overcome the problem of causal depth.</p>

Developmental noise is an overlooked contributor to innate variation in psychological traits

Stochastic developmental variation is an additional important source of variance – beyond genes and environment – that should be included in considering how our innate psychological predispositions may interact with environment and experience, in a culture-dependent manner, to ultimately shape patterns of human behaviour.

Phenotypic plasticity and developmental noise in hybrid and parental clones of Daphnia longispina complex

According to the “temporal hybrid superiority hypothesis”, seasonal variability in environmental factors in temperate lakes gives hybrid clones within the D. longispina complex a temporary fitness advantage, thus allowing long-term, dynamic coexistence of hybrids and maternal taxa. However, the maintenance of hybrids would not require their superiority under any given set of environmental conditions if their average fitness over longer periods surpassed that of more specialized and less flexible parental clones. Phenotypic plasticity and developmental noise of several hybrid and maternal clones of Daphnia (Daphnia galeata, Daphnia hyalina, their hybrids and backcrosses) were compared in a series of laboratory experiments. Changes in depth selection and body size at first reproduction were scored in Daphnia exposed to predator (planktivorous fish) threat, to the presence of filamentous cyanobacteria (Cylindrospermopsis raciborskii), and to the presence of toxic compounds (PCB52 and PCB153). The hybrid clones were found to exhibit the broadest phenotypic plasticity of the studied traits in response to the different stress factors. Developmental noise in depth selection behaviour was the lowest in Daphnia galeata, the highest in Daphnia hyalina, and intermediate in hybrid and backcross clones. This diversity of reaction norms might permit the coexistence of closely related Daphnia clones in the variable and often unpredictable lake environment.

Is There More to Within-plant Variation in Seed Size than Developmental Noise?

Within-plant variation in seed size may merely reflect developmental instability, or it may be adaptive in facilitating diversifying bet-hedging, that is, production of phenotypically diverse offspring when future environments are unpredictable. To test the latter hypothesis, we analyzed patterns of variation in seed size in 11 populations of the perennial vine Dalechampia scandens grown in a common greenhouse environment. We tested whether population differences in the mean and variation of seed size covaried with environmental predictability at two different timescales. We also tested whether within-plant variation in seed size was correlated with independent measures of floral developmental instability and increased under stressful conditions. Populations differed genetically in the amount of seed-size variation occurring among plants, among infructescences within plants, and among seeds within infructescences. Within-individual variation was not detectably correlated with measures of developmental instability and did not increase under stress, but it increased weakly with short-term environmental unpredictability of precipitation at the source-population site. These results support the hypothesis that greater variation in seed size is adaptive when environmental predictability is low.

Nature, Nurture, and Noise: Developmental Instability, Fluctuating Asymmetry, and the Causes of Phenotypic Variation

Phenotypic variation arises from genetic and environmental variation, as well as random aspects of development. The genetic (nature) and environmental (nurture) components of this variation have been appreciated since at least 1900. The random developmental component (noise) has taken longer for quantitative geneticists to appreciate. Here, I sketch the historical development of the concepts of random developmental noise and developmental instability, and its quantification via fluctuating asymmetry. The unsung pioneers in this story are Hugo DeVries (fluctuating variation, 1909), C. H. Danforth (random variation between monozygotic twins, 1919), and Sewall Wright (random developmental variation in piebald guinea pigs, 1920). The first pioneering study of fluctuating asymmetry, by Sumner and Huestis in 1921, is seldom mentioned, possibly because it failed to connect the observed random asymmetry with random developmental variation. This early work was then synthesized by Boris Astaurov in 1930 and Wilhelm Ludwig in 1932, and then popularized by Drosophila geneticists beginning with Kenneth Mather in 1953. Population phenogeneticists are still trying to understand the origins and behavior of random developmental variation. Some of the developmental noise represents true stochastic behavior of molecules and cells, while some represents deterministic chaos, nonlinear feedback, and symmetry breaking.

Dilp8 controls a time window for tissue size adjustment in Drosophila

ABSTRACTThe control of organ size mainly relies on precise autonomous growth programs. However, organ development is subject to random variations, called developmental noise, best revealed by the fluctuating asymmetry observed between bilateral organs. The developmental mechanisms ensuring bilateral symmetry in organ size are mostly unknown. In Drosophila, null mutations for the relaxin-like hormone Dilp8 increase wing fluctuating asymmetry, suggesting that Dilp8 plays a role in buffering developmental noise. Here we show that size adjustment of the wing primordia involves a peak of Dilp8 expression that takes place sharply at the end of juvenile growth. Wing size adjustment relies on a crossorgan communication involving the epidermis as the source of Dilp8. We identify ecdysone signaling as both the trigger for epidermal dilp8 expression and its downstream target in the wing primordia, thereby establishing reciprocal feedback between the two hormones as a systemic mechanism controlling organ size precision. Our results reveal a hormone-based time window ensuring fine-tuning of organ size and bilateral symmetry.