Body temperature (T(b)) profoundly affects the fitness of ectotherms. Many ectotherms use behavior to control T(b) within narrow levels. These temperatures are assumed to be optimal and therefore to match body temperatures (Trmax) that maximize fitness (r). We develop an optimality model and find that optimal body temperature (T(o)) should not be centered at Trmax but shifted to a lower temperature. This finding seems paradoxical but results from two considerations relating to Jensen's inequality, which deals with how variance and skew influence integrals of nonlinear functions. First, ectotherms are not perfect thermoregulators and so experience a range of T(b). Second, temperature-fitness curves are asymmetric, such that a T(b) higher than Trmax depresses fitness more than will a T(b) displaced an equivalent amount below Trmax. Our model makes several predictions. The magnitude of the optimal shift (Trmax - To) should increase with the degree of asymmetry of temperature-fitness curves and with T(b) variance. Deviations should be relatively large for thermal specialists but insensitive to whether fitness increases with Trmax ("hotter is better"). Asymmetric (left-skewed) T(b) distributions reduce the magnitude of the optimal shift but do not eliminate it. Comparative data (insects, lizards) support key predictions. Thus, "suboptimal" is optimal.

https://faculty.washington.edu/hueyrb/pdfs/MartinHuey08.pdf

Why “Suboptimal” Is Optimal: Jensen’s Inequality and Ectotherm Thermal Preferences

working knowledge of analysis of variance, correlation, and regression is probably necessary. However, calculus is not a prerequisite, nor is matrix algebra. When mathematical proofs are necessary, Falconer invariably uses a simple, satisfying, heuristic approach based on simple algebra or statistics. More importantly for students, Falconer provides easily understood, intuitive, and verbal explanations of why important results are true. Nowhere is this talent for simple explanations more evident than on page 62, where Falconer explains why small samples would be expected to exhibit an excess of heterozygotes relative to the Hardy-Weinberg expectations; this is not an easy concept to explain, but Falconer's explanation makes it seem self-evident. The foregoing account pertains to Introduction of Quantitative Genetics as a textbook. It should be emphasized that it is also an important book for professionals, as it gives an overview of quantitative genetics, its successes and its lacunae, by one of its preeminent investigators. A good textbook tells students merely what they should know. An excellent one tells them not only what they should know, but what a field is, what it has achieved, and where it is going; it provides a field's view of the world from inside itself at its present state of development; it is a review of a field by an author or authors skilled enough to know what to leave out. Introduction to Quantitative Genetics exemplifies these ideals to the highest degree. Introduction to Quantitative Genetics is an important book for another reason. In its outlook and examples it summarizes the collective experience and wisdom of the Edinburgh school of quantitative genetics (Falconer himself headed the Agricultural Research Council's Unit of Animals Genetics from 1968 until it was dissolved in 1980). Few would argue the proposition that this group of people represents an aggregation of the finest quantitative geneticists in the world-Falconer, A. Robertson, W. G. Hill, and many, many others throughout the years either on the staff or passing through as students, visitors, or scientists on sabbatical. Falconer's fine book is at once an exemplary textbook, an excellent summary of the field, and a tribute to the achievements of a creative and far-thinking group of quantitative geneticists. A noted human quantitative geneticist and friend of mine once said that the best possible objective with regard to Falconer's edition 1 was to set out to memorize it. I agree, and the same goes for edition 2.

Natural selection and social behavior

Animal diets crucially affect fitness, yet many aspects of their ultimate determinants are unknown. The distribution and extent of herbivory in lizards, its evolutionary history, and ecological factors that may favour it are discussed. Most lizards are exclusively or primarily carnivorous, yet many species eat some plants and a few are almost exclusively herbivorous. Based on a literature survey of diets of over 450 lizard species, the distribution and degree of omnivory and herbivory are described. Some plants occur in the diets of slightly over half of lizard species, and plants formed 10% or more of the dietary volume of 12.1% of species, and 90% or more of the diet of 0.8% of species. The greatest percentage of omnivorous species (> 10% plant diet), over 30% in each, and highest mean percentage plant matter in the diet are in Iguanidae, Corytophanidae, Gerrhosauridae, Agamidae, Xantusiidae, and Tropiduridae. Numerous other omnivores occur in Lacertidae and Scincidae and fewer in several additional families. Herbivorous lizards (> 90% plant volume) tend to be folivorous and to possess adaptations for processing leaves, including specialized dentition for cutting or reducing leaves, elongated intestines, colic valves that slow passage of food, and intestinal flora that digest cellulose. Omnivorous lizards lacking such specializations may eat some leaves, but consume much more fruit, flowers, and seeds, plant parts that are easy to digest, likely to be very abundant seasonally, and may be highly nutritious. Some lizards eat nectar and pollen; even sap is eaten by at least one gecko. Ontogenetic increase in plant consumption and decrease in prey consumption is known, but its generality has been controversial. Such ontogeny has been demonstrated in three iguanid species, a skink, a lacertid, two tropidurids, a phrynosomatid, and two corytophanids, but it does not occur in some other species. The importance of specific foods may vary with age. Omnivory and/or herbivory have originated in many lizard families, with at least nine origins in Iguania and 23 in Scleroglossa. Origins have been rare in Gekkonoidea and Anguimorpha and common in Scincomorpha, especially in Lacertidae and Scincidae. Losses of omnivory have been much less frequent than gains. Only a few origins can account for all the herbivory in lizards. Concentrated changes tests show that there is a significant association in Lacertidae, Lacertiformes, Lacertoidea, Scincidae, and Scleroglossa between insularity and omnivory. Insular lizards may broaden their diets to compensate for limited availability of prey. Addition of other factors that reduce availability of prey, i.e. extreme aridity and cave-dwelling, to insularity, strengthened the relationship to omnivory in Lacertidae and Lacertoidea. We were unable to demonstrate a role of aridity independent of insularity, but present anecdotal evidence suggests that it may promote evolution of plant consumption. Large body size in lizards has long been associated with herbivory, and more recently, with omnivory in lacertid lizards. Using a conventional regression approach in which each species is considered to supply an independent data point, this relationship was confirmed for all lizards. Although larger species have diets with more plants, plant consumption accounts for only 9% of the variation in body length, which is not surprising given that other factors such as predation, competition, and sexual selection affect body size. The frequency of transitions body size associated with transitions to omnivory or carnivory was also examined. In Iguania, Scleroglossa, and all lizards, transitions supporting the hypothesis that omnivory favours increase in body size were significantly more frequent than non-supporting transitions. This suggests that substantial plant consumption favours evolution of larger size, probably because of the energetic considerations first presented by Pough (1973). Because actively foraging lizards move widely through the habitat to locate prey and tongue-flick to locate prey by chemical cues, we hypothesized that they may be more likely to evolve omnivory than ambush foragers, which wait motionless for prey and do not tongue-flick to locate or identify prey. The basis of this prediction is that the wider seaching of active foragers predisposes them to contact with a greater variety and quantity of plants and that chemosensory tongue-flicking used by omnivores to identify plant food might be easier to evolve in active foragers that already use pre-chemical discrimination. The prediction is supported by a significantly greater per species frequency of origins of omnivory by active foragers than by ambushers. A scenario for the progressive evolution of omnivory and herbivory from ancestrally carnivorous lizards is discussed.

Distribution, extent, and evolution of plant consumption by lizards

Comparisons between closely related radiations in different environments provide a unique window into understanding how abiotic and biotic factors shape evolu- tionary pathways. Anolis lizards have radiated extensively in the West Indies, as well as mainland Central and South America. In the Caribbean, similar communities of anole species specialized for different habitats (ecomorphs) have evolved independently on each Greater Antillean island. We examined ecological and morphological data on 49 Anolis species (33 Caribbean, 16 mainland) to investigate whether the same set of ecomorphs has arisen in mainland regions. More generally, we investigated whether the relationship between ecology and morphology was similar among anoles in the two regions. Radiations in the two regions are very different. The majority of mainland anole species exhibit morphological characteristics unlike any Caribbean ecomorph. Furthermore, rela- tionships between ecology and morphology are very different between the two sets of anole species. Among mainland anole species, toepad size is positively correlated with perch height, whereas tail length is negatively related to perch diameter. In contrast, among Caribbean anole species, both forelimb length and body mass are positively associated with perch diameter, and both tail length and hindlimb length are negatively related to perch diameter. Biomechanical considerations provide a functional basis for some of these cor- relations, but much variation remains to be explained. These findings demonstrate that factors that caused anole species to converge repeatedly in the West Indies are not present in mainland regions, and that environmental factors can strongly influence the shape of evolutionary radiations.

https://www.jstor.org/stable/pdfplus/2265955.pdf

A comparison of evolutionary radiations in mainland and caribbean anolis lizards

Lizards and snakes putatively arose between the early Jurassic and late Triassic; they diversified worldwide and now occupy many different ecological niches, making them ideal for testing theories on the origin of ecological traits. We propose and test the “deep history hypothesis,” which claims that differences in ecological traits among species arose early in evolutionary history of major clades, and that present-day assemblages are structured largely because of ancient, preexisting differences. We combine phylogenetic data with ecological data collected over nearly 40 years to reconstruct the evolution of dietary shifts in squamate reptiles. Data on diets of 184 lizard species in 12 families from 4 continents reveal significant dietary shifts at 6 major divergence points, reducing variation by 79.8%. The most striking dietary divergence (27.6%) occurred in the late Triassic, when Iguania and Scleroglossa split. These two clades occupy different regions of dietary niche space. Acquisition of chemical prey discrimination, jaw prehension, and wide foraging provided scleroglossans access to sedentary and hidden prey that are unavailable to iguanians. This cladogenic event may have profoundly influenced subsequent evolutionary history and diversification. We suggest the hypothesis that ancient events in squamate cladogenesis, rather than present-day competition, caused dietary shifts in major clades such that some lizard clades gained access to new resources, which in turn led to much of the biodiversity observed today.

/pdf/deep-history-impacts-present-day-ecology-and-biodiversity-523ua447q6.pdf

Deep history impacts present-day ecology and biodiversity.

We investigated thermoregulation and habitat use in two sympatric lizard species of the family Phrynosomatidae (side-blotched lizards, Uta stansburiana, and sand-dune lizards, Sceloporus arenicolus...

Thermoregulatory accuracy, precision, and effectiveness in two sand-dwelling lizards under mild environmental conditions

Ontogenetic shifts from insect consumption by juveniles to plant consumption by adults are rare in the herbivorous lizard family Iguanidae. My investigations on diet and digestive tract anatomy of the iguanid lizard Ctenosaura pectinata show that this species has an ontogenetic diet shift. Insects were rare in adult diets but constituted 86.5% (by volume) of the food eaten by the smallest juveniles. All age classes ate some plant parts from a range of plant types, but flowers and leaves of legumes were a primarily food source. Non-adult lizards had the widest food niche breadths. Arthropods in the diet of juveniles and immatures covaried seasonally with the decline of arthropod abundance. Several hypotheses could explain this ontogenetic plasticity in diet. I rejected hypotheses that gut structure constrained juveniles to an arthropod diet and that insect consumption was purely an artifact of plant consumption because (1) size-adjusted gut morphology and capacity was similar among age classes, and (2) no food plants sampled had an excessive density of arthropods. I supported an alternative hypothesis that juveniles can eat plants but do not because insects provide a more nutritious diet. This conclusion was based on the observation that the juvenile hindgut is similar to that of herbivorous adults, and the propensity for juveniles to consume primarily, but not exclusively, insects when they were most abundant. The hindgut represents the site of fermentative plant fiber breakdown in many herbivorous lizards. Insect foods can compensate for size-related nutritional needs (energy and protein) and digestive limitations in juveniles. Opportunistic feeding to maintain a broad diet might help juvenile and immature lizards through high-predation-risk growth periods by reducing searching costs, increasing nutritional and energetic gains due to associative effects, and increasing new food exposure.

Ontogenetic plasticity of food habits in the Mexican spiny-tailed iguana, Ctenosaura pectinata.

The lizard Norops oxylophus used a variety of microhabitats distributed linearly along streams in southeastern Nicaragua. Body temperatures averaged 27.8 °C and lizards typically were in shade. Liz...

Ecology of the lizard Norops oxylophus (Polychrotidae) in lowland forest of southeastern Nicaragua

I tested the hypothesis that an animal with an ontogenetic diet shift must have different digestive efficiencies for foods that correspond to its diet shift, so that nutrient and energy extraction are maximized. The iguanine lizard Ctenosaura pectinata undergoes an ontogenetic diet shift from eating insects as a juvenile to plants as an adult. When fed six different pure foods from the natural diets of different age classes, C. pectinata assimilated nutrients and energy differently depending on food type and age class. Extraction of energy and nutrients in insect larvae was maximized by juvenile lizards. Calcium, phosphorus, and energy were readily assimilated from flowers and fruit by immature and adult lizards. Magnesium levels were highest in leaves and were extracted by immature and adult lizards, but xenobiotic effects of one plant leaf (Croton suberosus), eaten by adults, killed juvenile lizards. Although juvenile C. pectinata ate some flowers (Senna wislizenii) naturally, they were less ef...

https://www.jstor.org/stable/10.1086/383502

Ontogenetic Variation in Digestion by the Herbivorous Lizard Ctenosaura pectinata

We investigated the potential for ontogenetic resource partitioning within a population of the Texas earless lizard Cophosaurus texanus. Results from focal samples, line transects, haphazard observations, and stomach flushes compiled in summer (July 1993) and autumn (September 1995) revealed differences in microhabitat use and diet between adults and juveniles. Juveniles use rock perches more frequently than adult males, and consume smaller prey than adults. No ontogenetic differences in thermal ecology were observed. Diet differences between juveniles and adults may be attributed to the inability of juveniles to handle large prey items. Differences between juveniles and adults in prey size and microhabitat use suggest ontogenetic variation in foraging, predator avoidance, and territory defense.

Richard D. Durtsche

Papers

Thermoregulatory accuracy, precision, and effectiveness in two sand-dwelling lizards under mild environmental conditions

Ontogenetic plasticity of food habits in the Mexican spiny-tailed iguana, Ctenosaura pectinata.

Ecology of the lizard Norops oxylophus (Polychrotidae) in lowland forest of southeastern Nicaragua

Ontogenetic Variation in Digestion by the Herbivorous Lizard Ctenosaura pectinata

Ontogenetic variation in the autecology of the greater earless lizard Cophosaurus texanus