So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

Genetics and analysis of quantitative traits

I. the origin of species by means of natural selection

The decline of biodiversity with latitude has received great attention, but both the concise pattern and the causes of the gradient are under strong debate. Most studies of the latitudinal gradient comprise only one or few organism types and are often restricted to certain region or habitat types. To test for significant variation in the gradient between organisms, habitats, or regions, a meta-analysis was conducted on nearly 600 latitudinal gradients assembled from the literature. Each gradient was characterized by two effect sizes, strength (correlation coefficient) and slope, and additionally by 14 variables describing organisms, habitats, and regions. The analysis corroborated the high generality of the latitudinal diversity decline. Gradients on regional scales were significantly stronger and steeper than on local scales, and slopes also varied with sampling grain. Both strength and slope increased with organism body mass, and strength increased with trophic level. The body mass-effect size relation varied for ecto- versus homeotherm organisms and for different dispersal types, suggesting allometric effects on energy use and dispersal ability as possible mechanisms for the body mass effect. Latitudinal gradients were weaker and less steep in freshwater than in marine or terrestrial environments and differed significantly between continents and habitat types. The gradient parameters were not affected by hemisphere or the latitudinal range covered. This analysis is the first to describe these general and significant patterns, which have important consequences for models aiming to explain the latitudinal gradient.

/pdf/on-the-generality-of-the-latitudinal-diversity-gradient-1wj0z273b3.pdf

On the Generality of the Latitudinal Diversity Gradient

ION, GENERAL CONCEPTIONS, SELF-CONSCIOUSNESS, MENTAL INDIVIDUALITY. It would be very difficult for any one with even much more knowledge than I possess, to determine how far animals exhibit any traces of these high mental powers. This difficulty arises from the impossibility of judging what passes through the mind of an animal; and again, the fact that writers differ to a great extent in the meaning which they attribute to the above terms, causes a further difficulty. If one may judge from various articles which have been published lately, the greatest stress seems to be laid on the supposed entire absence in animals of the power of abstraction, or of forming general concepts. But when a dog sees another dog at a distance, it is often clear that he perceives that it is a dog in the abstract; for when he gets nearer his whole manner suddenly changes, if the other dog be a friend. A recent writer remarks, that in all such cases it is a pure assumption to assert that the mental act is not essentially of the same nature in the animal as in man. If either refers what he perceives with his senses to a mental concept, then so do both. (44. Mr. Hookham, in a letter to Prof. Max Muller, in the 'Birmingham News,' May, 1873.) When I say to my terrier, in an eager voice (and I have made the trial many times), "Hi, hi, where is it?" she at once takes it as a sign that something is to be hunted, and generally first looks quickly all around, and then rushes into the nearest thicket, to scent for any game, but finding nothing, she looks up into any neighbouring tree for a squirrel. Now do not these actions clearly shew that she had in her mind a general idea or concept that some animal is to be discovered and hunted? It may be freely admitted that no animal is self-conscious, if by this term it is implied, that he reflects on such points, as whence he comes or whither he will go, or what is life and death, and so forth. But how can we feel sure that an old dog with an excellent memory and some power of imagination, as shewn by his dreams, never reflects on his past pleasures or pains in the chase? And this would be a form of self-consciousness. On the other hand, as Buchner (45. 'Conferences sur la Theorie Darwinienne,' French translat. 1869, p. 132.) has remarked, how little can the hardworked wife of a degraded Australian savage, who uses very few abstract words, and cannot count above four, exert her self-consciousness, or reflect on the nature of her own existence. It is generally admitted, that the higher animals possess memory, attention, association, and even some imagination and reason. If these powers, which differ much in different animals, are capable of improvement, there seems no great improbability in more complex faculties, such as the higher forms of abstraction, and selfconsciousness, etc., having been evolved through the development and combination of the simpler ones. It has been urged against the views here maintained that it is impossible to say at what point in the ascending scale animals become capable of abstraction, etc.; but who can say at what age this occurs in our young children? We see at least that such powers

https://www.jstage.jst.go.jp/article/ase1887/22/257/22_257_458/_pdf

The descent of man and selection in relation to sex

It is widely agreed that fecundity selection and sexual selection are the major evolutionary forces that select for larger body size in most organisms. The general, equilibrium view is that selection for large body size is eventually counterbalanced by opposing selective forces. While the evidence for selection favoring larger body size is overwhelming, counterbalancing selection favoring small body size is often masked by the good condition of the larger organism and is therefore less obvious. The suggested costs of large size are: (1) viability costs in juveniles due to long development and/or fast growth; (2) viability costs in adults and juveniles due to predation, parasitism, or starvation because of reduced agility, increased detectability, higher energy requirements, heat stress, and/or intrinsic costs of reproduction; (3) decreased mating success of large males due to reduced agility and/or high energy requirements; and (4) decreased reproductive success of large females and males due to late reproduction. A review of the literature indicates a substantial lack of empirical evidence for these various mechanisms and highlights the need for experimental studies that specifically address the fitness costs of being large at the ecological, physiological, and genetic levels. Specifically, theoretical investigations and comprehensive case studies of particular model species are needed to elucidate whether sporadic selection in time and space is sufficient to counterbalance perpetual and strong selection for large body size.

/pdf/the-evolution-of-body-size-what-keeps-organisms-small-1yb7tgm94a.pdf

The evolution of body size: what keeps organisms small?

Two seemingly opposite evolutionary patterns of clinal variation in body size and associated life history traits exist in nature. According to Bergmann's rule, body size increases with latitude, a temperature effect. According to the converse Bergmann rule, body size decreases with latitude, a season length effect. A third pattern causally related to the latter is countergradient variation, whereby populations of a given species compensate seasonal limitations at higher latitudes by evolving faster growth and larger body sizes compared to their low latitude conspecifics. We discuss these patterns and argue that they are not mutually exclusive because they are driven by different environmental causes and proximate mechanisms; they therefore can act in conjunction, resulting in any intermediate pattern. Alternatively, Bergmann and converse Bergmann clines can be interpreted as over- and undercompensating countergradient variation, respectively. We illustrate this with data for the wide-spread yellow dung fly, Scathophaga stercoraria (Diptera: Scathophagidae), which in Europe shows a Bergmann cline for size and a converse Bergmann cline (i.e., countergradient variation) for development time. A literature review of the available evidence on arthropod latitudinal clines further shows a patterned continuum of responses. Converse Bergmann clines due to end-of-season time limitations are more common in larger species with longer development times. Our study thus provides a synthesis to the controversy about the importance of Bergmann's rule and the converse Bergmann rule in nature.

https://www.zora.uzh.ch/id/eprint/154217/1/ZORA_NL_154217.pdf

Bergmann and converse bergmann latitudinal clines in arthropods: two ends of a continuum?

SECTION I: MACRO-PATTERNS: EXPLAINING BROAD-SCALE PATTERNS OF VARIATION IN SEXUAL SIZE DIMORPHISM SECTION II: MICRO-PATTERNS: CASE STUDIES OF PATTERNS AND EVOLUTIONARY PROCESSES WITHIN AND AMONG SPECIES SECTION III: PROXIMATE DEVELOPMENTAL AND GENETIC MECHANISMS

Sex, size, and gender roles : evolutionary studies of sexual size dimorphism

(Invited Article)
Abstract
Sexual size dimorphism (SSD) is widespread and variable among animals. According to the differential equilibrium model, SSD in a given species is expected to result if opposing selection forces equilibrate differently in both sexes. Here I review the factors that affect the evolution of SSD specifically as they relate to behavior. Taking the approach that SSD results as an epiphenomenon from separate but related selection on male and female body size, the advantages and disadvantages of large size in terms of the standard components of individual fitness (mating success, fecundity, viability, growth, foraging success) are discussed to help guiding future research on the subject. This includes a discussion of intra-SSDs. The main conclusions are: (1) Evidence for disadvantages of large body size is still sparse and requires more research. In contrast, evidence for sexual or fecundity selection favoring large body size is overwhelming, so these mechanisms do no longer require special attention, but need to be documented nonetheless to acquire a complete picture. (2) Some hypotheses suggesting that small size is favored are not well investigated at all, because they apply only to some species or restricted situations, may be difficult to study, or have simply been disregarded. Evidence for these cryptic hypotheses is best revealed using experiments under multiple environmental (food, temperature, etc.) stresses with particularly well-suited model species. (3) The evolution of SSD ultimately depends on processes generating variation within as well as between the sexes, so studies should always investigate and report effects on both sexes separately, in addition to size-dependent effects within each sex; within sexes the key issue is whether small individuals under, over- or perfectly compensate their general fitness disadvantage. (4) Tests of several hypotheses should be integrated in case studies of well-suited model species to investigate selection on body size comprehensively. For example, all episodes of sexual selection (mate search, competition, pre- and post-copulatory choice) should be addressed in conjunction. Investigations of size-selective and sex-dependent predation should take the viewpoint of the prey rather than the predator to permit integration of effects throughout prey ontogeny generated by various predators with differing preferences. Comparative studies should also test multiple alternative hypotheses at the same time to permit stronger inference. (5) Experimental behavioral studies of sexual and natural selection should provide selection differentials using the available standard methods. This would allow integration with phenomenological studies of selection and facilitate subsequent meta-analyses, which are very valuable in evaluating general patterns. (6) Comparative phylogenetic studies identifying patterns and phenomenological and experimental studies of model species that investigate particular mechanisms should be integrated, so that macro-evolutionary patterns can be linked to micro-evolutionary processes, which is the central paradigm of evolutionary ecology. (7) A major problem is the general difficulty of separating causes generating a particular body size and SSD over evolutionary time and its consequences for behavior and ecology today, i.e. today's researchers cannot completely avoid this ‘ghost of SSD evolution past’.

Behavioral Causes and Consequences of Sexual Size Dimorphism

In the dry grass of a California meadow, the taut
spiral of an orb web catches the early morning sun.
A fat, yellow and black spider rests in the middle
of the web, a crazy zig-zag of white silk marking
the web below her (Figure 1.1). You stop and look
more closely. This is a female Argiope aurantia and
she is waiting for a morning meal. Her body is
almost 20 mm long, and she seems gigantic, with a
great round abdomen. Curiously, on the same web
a much smaller, thinner, less brightly coloured
spider seems to be moving cautiously toward the
waiting female. This is a mature male A. aurantia
and he is attempting to court the female and
induce her to mate with him. He is only a fraction
of her size (less than 6 mm long), and would easily
make a meal. However, if he is successful in
seducing her, he may fertilize all of the 300–400
eggs in her next egg sac, a worthy prize indeed
(Foellmer and Fairbairn 2004). This is a dangerous
enterprise for him because even if he escapes being
eaten he will surely die in the end, spontaneous
death during copulation being the fate of males of
this species (Foellmer and Fairbairn 2003, 2004).
Even to achieve his position close to the center of
the web, he has had to battle with other males
waiting for the female to become reproductively
mature. In this contest, larger males had the
advantage (Foellmer and Fairbairn 2005a) and yet
all of the males are much smaller than their
potential mate. Why is this?

/pdf/sex-size-and-gender-roles-5gb1yv4a0w.pdf

Wolf U. Blanckenhorn

Papers

The evolution of body size: what keeps organisms small?

Bergmann and converse bergmann latitudinal clines in arthropods: two ends of a continuum?

Sex, size, and gender roles : evolutionary studies of sexual size dimorphism

Behavioral Causes and Consequences of Sexual Size Dimorphism

Sex, Size and Gender Roles