Evolution Of Large Size Research Articles

Independent evolution toward larger body size in the distinctive Faroe Island mice.

Most phenotypic traits in nature involve the collective action of many genes. Traits that evolve repeatedly are particularly useful for understanding how selection may act on changing trait values. In mice, large body size has evolved repeatedly on islands and under artificial selection in the laboratory. Identifying the loci and genes involved in this process may shed light on the evolution of complex, polygenic traits. Here, we have mapped the genetic basis of body size variation by making a genetic cross between mice from the Faroe Islands, which are among the largest and most distinctive natural populations of mice in the world, and a laboratory mouse strain selected for small body size, SM/J. Using this F2 intercross of 841 animals, we have identified 111 loci controlling various aspects of body size, weight and growth hormone levels. By comparing against other studies, including the use of a joint meta-analysis, we found that the loci involved in the evolution of large size in the Faroese mice were largely independent from those of a different island population or other laboratory strains. We hypothesize that colonization bottleneck, historical hybridization, or the redundancy between multiple loci have resulted in the Faroese mice achieving an outwardly similar phenotype through a distinct evolutionary path.

Skeletal correlates of flight specialization in large birds and their application to extinct giants

This study addresses questions related to the size limits of flying birds and tradeoffs associated with the evolution of large size. Flight imposes unique limits on size in animals, and as such, form and function in large flyers can provide unique insights regarding the mechanical and physiological limits of vertebrate animals. We focused on specializations in skeletal morphology associated with the large size of flying birds. We developed a large comparative dataset of axial and appendicular skeletal proportions for living birds, using the collections of the Natural History Museum of Los Angeles County. We examined skeletal proportions because they provide mechanically relevant data and because of their applicability to fossil taxa. Some extinct, flight‐capable birds achieved sizes far exceeding that of any living flying birds. The ecologies and flight performance profiles of these extinct forms are a matter of debate. Our dataset and methodology address these questions related to flight capacity.We consider the implications of our results for three different extinct giant flying birds: pelagornithids, teratorns, and giant storks. The largest pelagornithids had wingspans of up to 6 meters, twice that of the largest span in living birds. The teratorns contain the largest flying birds in the world with wingspans potentially reaching 6.5 m, and masses up to 75 kg. The flight capability of Leptoptilos robustus, a giant stork from the Indonesian island of Flores, is largely debated. This animal was nearly 1.8 meters tall and likely massed over 16 kg.We took mechanically relevant skeletal measurements from over 300 living birds, focusing on the forelimb, hind limb, and sternal elements. Analysis of residuals from a series of linear regressions showed that large soaring specialists have significantly longer humeri compared to their sterna than other birds. This analysis also revealed that wing propelled swimmers and burst flyers tend to possess significantly shortened humeri. Burst adapted flyers, especially the largest burst specialists (wild turkeys), possess sterna that are significantly longer and deeper, relative to sternal width, than those of other birds. Interestingly, large wing‐propelled swimmers also have higher sternal length to width ratios than other birds. By contrast, soaring specialists have relatively “typical” sternal proportions, as indicated by small residuals in sternal length when regressed against sternal width.These results, taken together, indicate that relatively simple measurements of limb bone and sternum dimensions can be a powerful tool for distinguishing between burst adapted and soaring adapted large flyers. Since large flying animals rely on high fractions of anaerobic flight muscle to maintain sufficient mass‐specific power for flight, most large flyers specialize in either burst takeoff or soaring flight. Our methodology distinguishes between these specializations with a high degree of accuracy in living taxa. We propose the same approach can be used for fossil taxa. Preliminary application of our comparative metrics suggest that teratorns were less condor‐like in their flight performance profile than previously suggested and pelagornithids, while clearly soaring specialized, may have been marine thermal users, rather than dynamic soaring specialists.

Cajanus cajan (L.) Millsp.\xa0origins and domestication: the South and Southeast Asian archaeobotanical evidence

Cajanus cajan (L.) Millsp. commonly known as pigeonpea, red gram or gungo pea is an important grain legume crop, particularly in rain-fed agricultural regions in the semi-arid tropics, including Asia, Africa and the Caribbean. This paper provides a baseline for the study of the domestication and early history of C. cajan, through reviewing its modern wild distribution, seed morphometrics of wild and domesticated populations, historical linguistics and the archaeological record. The distribution of wild populations, including published records and additional herbarium collections, suggest that the wild habitats of pigeonpea were at the interface of the forest-edge areas and more open savanna plains in eastern Peninsular India (e.g. Telangana, Chattisgarh, Odisha). Early archaeological finds presented here have been recovered from both the Southern peninsula and Odisha. Historical linguistic data suggests early differentiation into longer and shorter growing season varieties, namely arhar and tuar types, in prehistory. Pigeonpea had spread to Thailand more than 2000 years ago. Measurements of seeds from modern populations provide a baseline for studying domestication from archaeological seeds. Available measurements taken on archaeological Cajanus spp. suggest that all archaeological collections thus far fall into a domesticated Length:Width ratio, while they may also pick up the very end of the trend towards evolution of larger size (the end of the domestication episode) between 3700 and 3200 years BP. This suggests a trend over time indicating selection under domestication had begun before 3700 years ago and can be inferred to have started 5000–4500 years ago.

How has the environment shaped geographical patterns of insect body sizes? A test of hypotheses using sphingid moths

AbstractAimWe mapped the geographical pattern of body sizes in sphingid moths and investigated latitudinal clines. We tested hypotheses concerning their possible environmental control, that is, effects of temperature (negative: temperature size rule or Bergmann's rule; positive: converse Bergmann rule), food availability, robustness to starvation during extreme weather and seasonality.LocationOld World and Australia/Pacific region.MethodsBody size data of 950 sphingid species were compiled and related to their distribution maps. Focusing on body length, we mapped the median and maximum size of all species occurring in 100 km grid cells. In a comparative approach, we tested the predictions from explanatory hypotheses by correlating species' size to the average environmental conditions encountered throughout their range, under univariate and multivariate models. We accounted for phylogeny by stepwise inclusion of phylogenetically informed taxonomic classifications into hierarchical random‐intercept mixed models.ResultsMedian body sizes showed a distinctive geographical pattern, with large species in the Middle East and the Asian tropics, and smaller species in temperate regions and the Afrotropics. Absolute latitude explained very little body size variation, but there was a latitudinal cline of maximum size. Species' median size was correlated with net primary productivity, supporting the food availability hypothesis, whereas support for other hypotheses was weak. Environmental correlations contributed much less (i.e. <10%) to explaining overall size variation than phylogeny (inclusion of which led to models explaining >70% of variability).Main conclusionThe intuitive impression of larger species in the tropics is shaped by larger size maxima. Median body sizes are only very weakly related to latitude. Most of the geographical variation in body size in sphingid moths is explained by their phylogenetic past. NPP and forest cover correlate positively with the body size, which supports the idea that food availability allowed the evolution of larger sizes.

A Tyrannosauroid from the Lower Cenomanian of New Jersey and Its Evolutionary and Biogeographic Implications

The Barremian through Turonian record of tyrannosauroids in North America is sparse, and neither the western nor eastern portions of the continent have produced substantial material of early tyrant dinosaurs. This is unfortunate, as the discovery and description of several new tyrannosauroid genera from this temporal interval in recent years has shown that this period of time was likely when the tyrannosauroids evolved many of the signature features of the large- bodied genera that famously roamed the planet during the latest Cretaceous. One particular trait of the younger tyrant dinosaur genera that seems to have evolved during the aforementioned temporal interval was that of large body size. Here, I describe the metatarsal II of an indeterminate tyrannosauroid from the Cenomanian Potomac Formation of New Jersey. The metatarsal II is significant for several reasons. It is the only definite occurrence of a tyrannosauroid in eastern North America (Appalachia) before the Coniacian and Santonian and indicates an animal in the size range of tyrannosauroids from the Santonian to Maastrichtian of the Cretaceous. The New Jersey specimen thus differs from other, mostly small and gracile, known tyrannosaur genera of the mid-Cretaceous, suggesting that the evolution of large size among tyrannosauroids was a complex process. The metatarsal has morphological affinities to the corresponding metatarsal II of Appalachiosaurus montgomeriensis, and along with the results of phylogenetic analysis this suggests that Late Cretaceous Appalachian tyrannosauroids were relict forms isolated on the landmass.

Evolution of tolerance in an invasive weed after reassociation with its specialist herbivore.

The interaction between the European wild parsnip Pastinaca sativa and its coevolved florivore the parsnip webworm Depressaria pastinacella, established in North America for over 150 years, has resulted in evolution of local chemical phenotype matching. The recent invasion of New Zealand by webworms, exposing parsnips there to florivore selection for the first time, provided an opportunity to assess rates of adaptive response in a real-time experiment. We planted reciprocal common gardens in the USA and NZ with seeds from (1) US populations with a long history of webworm association; (2) NZ populations that had never been infested and (3) NZ populations infested for 3 years (since 2007) or 6 years (since 2004). We measured impacts of florivory on realized fitness, reproductive effort and pollination success and measured phenotypic changes in infested NZ populations relative to uninfested NZ populations to determine whether rapid adaptive evolution in response to florivory occurred. Irrespective of country of origin or location, webworms significantly reduced plant fitness. Webworms reduced pollination success in small plants but not in larger plants. Although defence chemistry remained unchanged, plants in infested populations were larger after 3-6 years of webworm florivory. As plant size is a strong predictor of realized fitness, evolution of large size as a component of florivore tolerance may occur more rapidly than evolution of enhanced chemical defence.

Deja vu: the evolution of feeding morphologies in the Carnivora

The fossil record of the order Carnivora extends back at least 60 million years and documents a remarkable history of adaptive radiation characterized by the repeated, independent evolution of similar feeding morphologies in distinct clades. Within the order, convergence is apparent in the iterative appearance of a variety of ecomorphs, including cat-like, hyena-like, and wolf-like hypercarnivores, as well as a variety of less carnivorous forms, such as foxes, raccoons, and ursids. The iteration of similar forms has multiple causes. First, there are a limited number of ways to ecologically partition the carnivore niche, and second, the material properties of animal tissues (muscle, skin, bone) have not changed over the Cenozoic. Consequently, similar craniodental adaptations for feeding on different proportions of animal versus plant tissues evolve repeatedly. The extent of convergence in craniodental form can be striking, affecting skull proportions and overall shape, as well as dental morphology. The tendency to evolve highly convergent ecomorphs is most apparent among feeding extremes, such as sabertooths and bone-crackers where performance requirements tend to be more acute. A survey of the fossil record indicates that large hypercarnivores evolve frequently, often in response to ecological opportunity afforded by the decline or extinction of previously dominant hypercarnivorous taxa. While the evolution of large size and carnivory may be favored at the individual level, it can lead to a macroevolutionary ratchet, wherein dietary specialization and reduced population densities result in a greater vulnerability to extinction. As a result of these opposing forces, the fossil record of Carnivora is dominated by successive clades of hypercarnivores that diversify and decline, only to be replaced by new hypercarnivorous clades. This has produced a marvelous set of natural experiments in the evolution of similar ecomorphs, each of which start from phylogenetically and morphologically unique positions.

The evolution of large size: how does Cope's Rule work?

Cope's Rule is the tendency for organisms in evolving lineages to increase in size over time. The concept is detailed in many textbooks, but has rarely been demonstrated. Many suggestions of the benefits of large body size exist, but none has yet been confirmed empirically. Using a large-scale analysis of recent studies, Kingsolver and Pfennig have now shown how size benefits survival, mating success and fecundity, and they provide convincing arguments for a mechanism that is capable of driving Cope's Rule.

Cope's rule, hypercarnivory, and extinction in North American canids.

Over the past 50 million years, successive clades of large carnivorous mammals diversified and then declined to extinction. In most instances, the cause of the decline remains a puzzle. Here we argue that energetic constraints and pervasive selection for larger size (Cope's rule) in carnivores lead to dietary specialization (hypercarnivory) and increased vulnerability to extinction. In two major clades of extinct North American canids, the evolution of large size was associated with a dietary shift to hypercarnivory and a decline in species durations. Thus, selection for attributes that promoted individual success resulted in progressive evolutionary failure of their clades.

Vestiges of a beginning? Paleontological and geochemical constraints on early animal evolution

Inspired by molecular clock estimates, some biologists have proposed that animals in general, and bilaterian metazoans in particular, began to diverge substantially earlier than fossils indicate. Balavoine and Adoutte [Science 280 (1998) 397] specifically hypothesized that the Cambrian explosion documents parallel radiations within three major bilaterian clades that diverged from one another relatively early in the Neoproterozoic Era. The geological record is permissive with respect to such hypotheses, but not encouraging. The earliest evolution of animals certainly took place before the initial appearance of phosphatic animal microfossils or Ediacaran macrofossils, but bilaterian clades need not have been part of this metazoan “pre-history”. Alternatively, the evolution of large size, made possible by late Neoproterozoic oxygen increase, may have provided the selective environment in which stem bilaterians differentiated. Cambrian events per se appear to have begun in the wake of environmental perturbation and accompanying extinction near the Proterozoic–Cambrian boundary.

Selective and genetic constraints on the evolution of body size in a stream-dwelling salmonid fish.

To examine constraints on evolution of larger body size in two stunted populations of brook charr (Salvelinus fontinalis) from a single river in Cape Race, Newfoundland, Canada, we measured viability selection acting on length-at-age traits, and estimated quantitative genetic parameters in situ (following reconstruction of pedigree information from microsatellite data). Furthermore we tested for phenotypic differentiation between the populations, and for association of high juvenile growth with early maturity that is predicted by life history theory. Within each population, selection differentials and estimates of heritabilities for length-at-age traits suggested that evolution of larger size is prevented by both selective and genetic constraints. Between the populations, phenotypic differentiation was found in length-at-age and age of maturation traits, whereas early maturation was associated with increased juvenile growth (relative to adult growth) both within and between populations. The results suggest an adaptive plastic response in age of maturation to juvenile growth rates that have a largely environmental basis of determination.

Parallel gigantism and complex colonization patterns in the Cape Verde scincid lizards Mabuya and Macroscincus (Reptilia: Scincidae) revealed by mitochondrial DNA sequences.

The scincid lizards of the Cape Verde islands comprise the extinct endemic giant Macroscincus coctei and at least five species of Mabuya, one of which, Mabuya vaillanti, also had populations with large body size. Phylogenetic analysis based on DNA sequences derived from the mitochondrial cytochrome b, cytochrome oxidase I and 12S rRNA genes (711, 498 and 378 base pairs (bp), respectively) corroborates morphological evidence that these species constitute a clade and that Macroscincus is unrelated to very large skinks in other areas. The relationships are ((M. vaillanti and Mabuya delalandii) (Mabuya spinalis and Macroscincus coctei (Mabuya fogoensis nicolauensis (Mabuya fogoensis antaoensis and Mabuya stangeri)))). The Cape Verde archipelago was colonized from West Africa, probably in the Late Miocene or Early Pliocene period. The north-eastern islands were probably occupied first, after which the ancestor of M. vaillanti and M. delalandii may have originated on Boavista, the ancestor of the latter species arriving on Santiago or Fogo later. The M. fogoensis--M. stangeri clade colonized the islands of Branco, Razo, Santa Luzia and São Vicente from São Nicolau and reached Santo Antão after this. Colonization of these northeastern islands was slow, perhaps because the recipient islands had not developed earlier or because colonization cut across the path of the Canary Current and the Northeast Trade Winds, the main dispersing agents in the region. Rapid extension of range into the southwestern islands occurred later in M. spinalis and then in M. vaillanti and M. delalandii. The long apparent delay between the origin of these species and their southwestern dispersal may have been because there were earlier colonizations of the southern islands which excluded later ones until the earlier inhabitants were exterminated by volcanic or climatic events. The evolution of large size in Macroscincus occurred in the northwestern islands and was paralleled in the eastern and southern islands by populations of M. vaillanti. Both cases of size increase in Cape Verde skinks were accompanied by the development of herbivory.