Small Adult Size Research Articles

Bioarchaeological Evidence for the Basis of Small Adult Stature in Southern Africa

Natural selection for small adult body size may be directly linked to various factors that differ by global region. Indirect selection through early cessation of growth has been postulated for pygmy groups. Small adult body size was maintained throughout the Holocene by the ancestors of the KhoeSan groups, Later Stone Age hunter-gatherers who lived in the coastal and near-coastal regions of South Africa. Contextual information from 134 burials of juveniles (76 with radiocarbon dates) is combined with assessment of child growth. Both timing of cessation of growth and patterns of juvenile mortality are pertinent to questions about the possible selective value of smallness. Later Stone Age juveniles who had dental ages in the midteen years had not yet achieved adult size; hence, early cessation of growth is not evident. For the period between ca. 3800 and 1800 BP, which was a time of increased variability in adult body size, there are more burials of older juveniles. The variability in the mortality profile suggests fluctuations in the rates of juvenile mortality rather than consistently high rates. We conclude that small body size had been established by the Holocene, and we suggest that its maintenance is linked to direct rather than indirect selection.

Dinosaur Census Reveals Abundant Tyrannosaurus and Rare Ontogenetic Stages in the Upper Cretaceous Hell Creek Formation (Maastrichtian), Montana, USA

BackgroundA dinosaur census recorded during the Hell Creek Project (1999–2009) incorporates multiple lines of evidence from geography, taphohistory, stratigraphy, phylogeny and ontogeny to investigate the relative abundance of large dinosaurs preserved in the Upper Cretaceous Hell Creek Formation of northeastern Montana, USA. Overall, the dinosaur skeletal assemblages in the Hell Creek Formation (excluding lag-influenced records) consist primarily of subadult or small adult size individuals. Small juveniles and large adults are both extremely rare, whereas subadult individuals are relatively common. We propose that mature individuals of at least some dinosaur taxa either lived in a separate geographic locale analogous to younger individuals inhabiting an upland environment where sedimentation rates were relatively less, or these taxa experienced high mortality before reaching terminal size where late stage and often extreme cranial morphology is expressed.Methodology/Principal Findings Tyrannosaurus skeletons are as abundant as Edmontosaurus, an herbivore, in the upper Hell Creek Formation and nearly twice as common in the lower third of the formation. Smaller, predatory dinosaurs (e.g., Troodon and dromaeosaurids) are primarily represented by teeth found in microvertebrate localities and their skeletons or identifiable lag specimens were conspicuously absent. This relative abundance suggests Tyrannosaurus was not a typical predator and likely benefited from much wider food choice opportunities than exclusively live prey and/or specific taxa. Tyrannosaurus adults may not have competed with Tyrannosaurus juveniles if the potential for selecting carrion increased with size during ontogeny.Conclusions/Significance Triceratops is the most common dinosaur and isolated skulls contribute to a significant portion of this census. Associated specimens of Triceratops consisting of both cranial and postcranial elements remain relatively rare. This rarity may be explained by a historical collecting bias influenced by facies and taphonomic factors. The limited discovery of postcranial elements may also depend on how extensive a fossil quarry is expanded after a skull is collected.

Reproductive strategy of the semelparous clam Gaimardia bahamondei (Bivalvia, Gaimardiidae)

Abstract. Semelparity is one of the most drastic reproductive strategies found among marine invertebrates. It is frequently found in species whose members have small adult sizes and brood embryos internally. In this study, we describe the reproductive strategy of the bivalve Gaimardia bahamondei to explore the possible causes of the association between semelparity and internal brooding. Males of this species exhibit continuous gonadal activity throughout the breeding season. Apparently continuous spawning of sperm is associated with an abundance of captured sperm in the adfrontal region of the gill filaments of both males and females. Females are capable of brooding three cohorts of embryos simultaneously while also producing three new cohorts of oocytes. This suggests that females are able to generate at least six cohorts of embryos during the breeding season. Embryos are brooded in the suprabranchial chamber and are individually surrounded by a membrane with a projecting peduncle; embryos are anchored by this peduncle to the adfrontal region of the gill filaments. Members of the youngest cohort differ in size, color, and shell ornamentation from members of the two older cohorts. There is no difference between members of the two older cohorts in size, but there is with respect to coloring and shell ornamentation. The importance of the embryonic cohorts in terms of their percentage of the total number of embryos varied among brooding females, suggesting among-female variation in the timing of release of the oldest cohort of embryos. Members of this cohort break loose from the gills, lose their surrounding membrane, and fall into the ventral region of the suprabranchial chamber, from which they are evacuated to the exterior. Continuous sperm production in males and the production of at least six cohorts of embryos in females suggest that the costs of reproduction are high, which may partly explain the semelparity identified in this species.

Invertebrate mesopredators are larger in streams with fish

Species with complex life cycles (e.g., aquatic larvae, terrestrial adults) are expected to shorten the time spent in the larval stage if mortality risks are high, a trade-off that lowers predation risk at the cost of reduced time for growth and thus smaller adult size. We tested these predictions by comparing the timing of and size at emergence for two relatively large and common invertebrate mesopredator species (Isoperla montana and Rhyacophila vibox) that inhabit small coastal streams, with and without predatory fish, in eastern Canada. Contrary to expectations based on predation risk–foraging trade-off theory, individuals of both invertebrate species tended to be larger rather than smaller in streams with fish than in fishless streams. The patterns were consistent, however, with the expected ecological effects of top predators on food webs, where fish lower abundances of invertebrate mesopredators, increasing resource availability and thus growth rates for the remaining individuals. We conclude that variation among streams in size at emergence is better explained by the impact of fish on resource availability than to behavioural or life history trade-offs occurring under risk of predation.

Depth as an organizer of fish assemblages in floodplain lakes

Depth reduction is a natural process in floodplain lakes, but in many basins has been accelerated by anthropogenic disturbances. A diverse set of 42 floodplain lakes in the Yazoo River Basin (Mississippi, USA) was examined to test the hypothesis of whether depth reduction was a key determinant of water quality and fish assemblage structure. Single and multiple variable analyses were applied to 10 commonly monitored water variables and 54 fish species. Results showed strong associations between depth and water characteristics, and between depth and fish assemblages. Deep lakes provided less variable environments, clearer water, and a wider range of microhabitats than shallow lakes. The greater environmental stability was reflected by the dominant species in the assemblages, which included a broader representation of large-body species, species less tolerant of extreme water quality, and more predators. Stability in deep lakes was further reflected by reduced among-lake variability in taxa representation. Fish assemblages in shallow lakes were more variable than deep lakes, and commonly dominated by opportunistic species that have early maturity, extended breeding seasons, small adult size, and short lifespan. Depth is a causal factor that drives many physical and chemical variables that contribute to organizing fish assemblages in floodplain lakes. Thus, correlations between fish and water transparency, temperature, oxygen, trophic state, habitat structure, and other environmental descriptors may ultimately be totally or partly regulated by depth. In basins undergoing rapid anthropogenic modifications, local changes forced by depth reductions may be expected to eliminate species available from the regional pool and could have considerable ecological implications.

Resurrection of Porites hawaiiensis Vaughan, 1907; a Hawaiian coral obscured by small size, cryptic habitat, and confused taxonomy

The purpose of this note is to propose recognition of Porites hawaiiensis Vaughan, 1907, (Figure 1A–D) a species currently regarded as a junior synonym of Porites rus (Forskål 1775), as a valid species, based on molecular and morphological characteristics. Vaughan (1907 p. 217, pl 91 figs 2, 2a) described Porites (Synaraea) hawaiiensis from a specimen collected from Kalihi Harbor on the island of O‘ahu, Hawai‘i (Figure 1 C). Porites (Synarea) hawaiiensis was also reported from the Marshall Islands by Wells (1954 p. 455, pl 170 figs 6,7). Porites hawaiiensis was subsequently thought to be a junior synonym of Porites (Synaraea) convexa Verrill, 1864, due to the small calices that are characteristic of the subgenus Synaraea (Maragos 1977). Later both species were made synonyms of P. (Synaraea) rus, Forskål 1775 (Veron & Pichon 1982; Cairns 1991). Vaughan, 1907 described the calices of P. hawaiiensis as “densely spinulose” with “coenchyma” equaling, or exceeding the 0.5 mm diameter of the calices, and a pitted star shaped space between the pali (Figure 1C,D). In the absence of living specimens, the Vaughan, 1907 type specimen was difficult to distinguish from newly settled P. rus colonies, but upon closer examination in the field, Maragos et al. (2004) recognized small coral colonies that appeared to match the description of P. hawaiiensis. This species can readily be distinguished from Porites rus and other Porites by very small colony size (<10cm), mottled yellow and green-brown coloration, encrusting form, and thicket of spiny denticles between distantly spaced corallites (Figure 1A–D). Genetic data from Forsman et al. 2009 confirmed that this small ‘patch coral’ is distinct from P. rus (n = 3 of each species; uncorrected pair-wise distance; mtCOI = 0.5% ± 0.2 SE; mtCR = 0.7%, and nuclear ITS = 14.2 % ± 1.3 SE), and is also distinct from all other Hawaiian congeners. The genetic data further indicated that ‘Synaraea’ was surprisingly closely related to other Poritids and may not warrant sub-genus status (Forsman et al. 2009). Fenner (2005) referred to this same small ‘patch coral’ as Porites cf. bernardi, however; P. bernardi Vaughan, 1907 type specimens were coralliths (Figure 1E) with calices similar in size to those of most other Porites (Figure 1 F). The geographic range of Porites hawaiiensis is unknown, although it is abundant throughout the Northwest and Main Hawaiian Islands, and has been reported at depths from 1 to 55m (30 fathoms) in the Marshall Islands (Wells 1954). This species can be easily overlooked; it tends to grow in cryptic habitats (cracks, crevices, and interstitial spaces), and at first glance, the small patches of colonies (0.5–10cm) can be confused with crustose coralline algae, or new recruits of other Porites species. This species is remarkable because of its small adult colony size; a curious life history characteristic since many Porites in the Pacific can be among the largest and longest-lived scleractinain corals (Brown et al. 2009). We propose that this small ‘patch coral’ is a distinct species, and that P. hawaiiensis is the most appropriate name.

Isopentenyl Transferase and Cytokinin Oxidase/Dehydrogenase Gene Family Members are Differentially Expressed During Pod and Seed Development in Rapid-cycling Brassica

The plant hormone group, the cytokinins, regulates many stages of plant growth and development. Regulation includes that of cell division and enhancement of sink strength, both of which are important processes in seed development and embryonic growth. Two gene families play a key role in maintaining cytokinin homeostasis: isopentenyl transferase (IPT), which catalyzes the rate-limiting step in the formation of cytokinins, and cytokinin oxidase/dehydrogenase (CKX), which irreversibly inactivates cytokinins by cleaving the N6 side chain. Quantitative reverse transcriptase polymerase chain reaction (PCR) was used to measure the expression of individual gene family members to investigate the source of cytokinin and its subsequent inactivation during the early stages of seed and pod development. In this study, rapid-cycling Brassica rapa (RCBr) was used because of its genetic relatedness to commercial Brassica species, its rapid life cycle, its small adult size, and its larger reproductive organs compared to Arabidopsis. Our results indicate that BrIPT1, -3, and -5 and BrCKX1, -2, -3, and -5 express differentially both temporally and spatially within RCBr root, stem, leaf, seed, and pod tissues. Particularly strong expression was shown by IPT3 and IPT5 and CKX2 in developing seeds.

Redescription of the striped catfish Mystus carcio (Hamilton) (Siluriformes: Bagridae)

Pimelodus carcio, originally described in 1822 by Francis Hamilton, has long been treated as a junior synonym of either Mystus tengara or M. vittatus. In this paper we revalidate and redescribe the species and diagnose it from other striped Mystus by the following combination of characters: small adult size, maturing at 44.0 mm standard length; adipose-fin base shorter than or equal to dorsal-fin base; pelvic fin reaching anal-fin origin; pectoral girdle with coracoid shield exposed ventro-laterally below pectoral fin; eyes rounded and large, dorsally orientated on head; vomerine tooth-patch interrupted at midline. The species is distributed in the Ganga-Brahmaputra drainage of northeast India and Bangladesh.

Growth and reproduction of Loxechinus albus (Echinodermata: Echinoidea) at the southerly peripheries of their species range, Falkland Islands (South Atlantic)

Sea urchins Loxechinus albus were collected from an unfished population inhabiting inshore areas of the eastern part of the Falkland Islands (Southwest Atlantic) at bimonthly intervals between January 2005 and March 2006. The gonads of 491 specimens were sampled to ascertain GSI, and a subsample was examined microscopically in order to determine sex and maturity stage. Age was determined by ring counts on genital plates of 349 specimens with the annual periodicity of ring deposition validated by marginal increment analysis. This investigation suggests that the study population spawns at the warmest time of the year thus allowing for greater growth in their pelagic larvae and newly settled juveniles. Size at age data were found to be asymptotic and out of three growth functions tested the von Beralanffy growth model best described the data. The relatively short period of optimal water temperatures around the Falkland Islands does not enable L. albus to grow as fast as in other regions with higher seasonal temperatures (central Chilean coasts) resulting in relatively small adult sizes.

Reply to Meiri and Raia: Small offspring size and fast life history all the way?

In an alternative approach to interpreting the developmental traits we described for the fossil insular bovid Myotragus (1), Meiri and Raia (2) aim to explain the slow and cyclical growth, the small offspring and adult size, and the many old individuals as a result of a shift toward a fast life-history and an accelerated reproduction to enhance fitness, which they feel is consistent with a scenario of reduced extrinsic mortality.

Henricia pumila sp. nov.: A brooding seastar (Asteroidea) from the coastal northeastern Pacific

A small species of the seastar genus Henricia Gray, 1840 occurs along the cool temperate Pacific coast of North America from near Sitka, Alaska to just south of Ensenada, Baja California, Mexico. Its small adult size, mottled aboral colors, and benthic external brooding reproductive mode have long been noted, but it has never been formally separated from the larger, free-spawning Henricia leviuscula (Stimpson, 1857), with which it has been confused. Here we amplify the description of H. leviuscula, based on examination of the holotype and new specimens, and restrict it to only one of several similar species that co-occur in Puget Sound and vicinity. We also describe the small mottled brooder as Henricia pumila sp. nov., characterize its distribution, and contrast its morphology with H. leviuscula based on the arrangement of marginal plates and the microanatomy of aboral spines.

First report of Blanford's semaphore gecko, Pristurus rupestris (Blanford 1874) (Sauria: Gekkonidae) in Fars Province, Iran

Pristurus Ruppel, 1835 is a gekkonine genus having many adaptations in common with the New World sphaerodactyline gecko, viz., diurnal habits, sexual dichromatism, round pupil, eyelid formed by circumorbital ring of tissue, simple undilated digits as in Gonatodes, small adult size, lack of preanal pores, lack of cloacal sacs and bones, and loss of splenial (Kluge, 1967; 1983). Its distribution is on islands and coastal regions of eastern Africa, Arabia, and Southeast Asia bordering the Red Sea, Gulf of Oman, and the Persian Gulf (Anderson, 1999). This genus comprises about 22 species, 14 inhabiting the Western Palearctic (Sindaco and Jeremcenko, 2008). Blanford's semaphore gecko, Pristurus rupestris was reported for the first time by Blanford in 1874 in Muscat, Oman (Leviton et al., 1992; Anderson, 1999). This species is distributed in the Arabian Peninsula (north to southwest Jordan), the Persian Gulf coast of Iran, Eritrea, Djibouti, and north of Somalia (including the border with Ethiopia) (Sindaco and Jeremcenko, 2008). Anderson (1999) reported this species in nine localities including Bandar-eLengeh, Bushehr, Cheh Mossulum, Tangistan, Jask, Minab, the Genu protected region, Chah Bahar, Khark Island, and Qeshm Island. Reports of Rastegar Pouyani et al. (2006) expanded the distribution of this species to Sistan and Baluchistan province. In summer and winter of 2007 and spring 2008, 4 specimens of this species were collected: two in Demaghah-IGora in southwest Fars Province, southwest Iran (27o 28'N, 53o 2'E; 421 m) (Fig. 1), about 1 km northwest of Varavi town, 25 km from the city of Lamerd, and two specimens in the northeast of it on the wall of a house on a mountainside). These specimens were captured on the limestone rock surfaces of mountains, the stone walls of palm groves (Fig. 2), and on the cement wall of a house adjacent to the mountain. Hence the distribution of this species expands into Fars Province. This locality is about 200 km from the nearest previously published record.

Description and Phylogenetic Relationships of Two New Species of Miniature Arthroleptis (Anura: Arthroleptidae) from the Eastern Arc Mountains of Tanzania

I describe two new species of squeaker frog (Arthroleptidae: Arthroleptis) from the Eastern Arc Mountains of Tanzania. These new species are distinguished from other miniature Arthroleptis in the Eastern Arc Mountains by the combination of very small adult body size (< 15 mm snout–vent length), a pronounced dark inguinal spot, and color patterns unique to each species. The new species could be the smallest frog species known from East Africa and among the smallest species of Arthroleptis. An estimate of phylogeny on the basis of mitochondrial DNA sequences reveals that these morphologically cryptic species are sister taxa that compose a basal lineage within a clade of miniature Arthroleptis. Their description hints at a diverse cryptic amphibian fauna in the Eastern Arc Mountains that awaits additional discovery through molecular methods.

Viability selection on early body mass and the effect of female body size on fecundity: a study on the leaf‐eared mouse Phyllotis darwini

AbstractViability selection and fecundity of size‐related traits has been demonstrated to be strong in vertebrates. In small mammals, both offspring and adult size are important for viability and fecundity, respectively. We studied the role of early phenotypic selection on size attributes and female fecundity in the leaf‐eared mouse (Phyllotis darwini). Our results support that larger females produce more offspring, and since the likelihood of attaining adulthood is similar for different sizes of the females, those larger females also produce more offspring that attain sexual maturity. From the offspring perspective, larger pups at birth have significantly more probability of attaining sexual maturity. However, weaning mass and growth rate did not show any differential survival. Our study suggests that early selection could be important and could prevent further episodes of selection by early culling of the distribution of sizes, and that “effective” fecundity is strongly dependent on the size of the female.

Brain IGF-1 Receptors Control Mammalian Growth and Lifespan through a Neuroendocrine Mechanism

Mutations that decrease insulin-like growth factor (IGF) and growth hormone signaling limit body size and prolong lifespan in mice. In vertebrates, these somatotropic hormones are controlled by the neuroendocrine brain. Hormone-like regulations discovered in nematodes and flies suggest that IGF signals in the nervous system can determine lifespan, but it is unknown whether this applies to higher organisms. Using conditional mutagenesis in the mouse, we show that brain IGF receptors (IGF-1R) efficiently regulate somatotropic development. Partial inactivation of IGF-1R in the embryonic brain selectively inhibited GH and IGF-I pathways after birth. This caused growth retardation, smaller adult size, and metabolic alterations, and led to delayed mortality and longer mean lifespan. Thus, early changes in neuroendocrine development can durably modify the life trajectory in mammals. The underlying mechanism appears to be an adaptive plasticity of somatotropic functions allowing individuals to decelerate growth and preserve resources, and thereby improve fitness in challenging environments. Our results also suggest that tonic somatotropic signaling entails the risk of shortened lifespan.

Reduced learning ability as a consequence of evolutionary adaptation to nutritional stress in Drosophila melanogaster

Abstract 1. Dietary conditions affect cognitive abilities of many species, but it is unclear to what extent this physiological effect translates into an evolutionary relationship.2. A reduction of competitive ability under nutritional stress has been reported as a correlated response to selection for learning ability in Drosophila melanogaster. Here we test whether the reverse holds as well, i.e. whether an evolutionary adaptation to poor food conditions leads to a decrease in learning capacities.3. Populations of D. melanogaster were: (i) not subject to selection (control), (ii) selected for improved learning ability, (iii) selected for survival and fast development on poor food, or (iv) subject to both selection regimes.4. There was no detectable response to selection for learning ability.5. Selection on poor food led to higher survival, faster development and smaller adult size as a direct response, and to reduced learning ability as a correlated response. This study supports the hypothesis that adaptation to poor nutrition is likely to trade off with the evolution of improved learning ability.

Powelliphanta augusta, a new species of land snail, with a description of its former habitat, Stockton coal plateau, New Zealand

A recently discovered and threatened large land snail, Powelliphanta augusta n. sp. is described from Mt Augustus on the western scarp of the Stockton Plateau, North Westland. On shell characters it is readily distinguishable from all other Powelliphanta, with narrow red spiral lines underlying irregular and variable dark reddish‐brown axial bands, a small adult size and sculptured dorsal surface. Differences in the shell morphology of P. augusta, its closest phylogenetic relative P. lignaria, and its closest geographic neighbour P. patrickensis, were investigated using principal components analysis. P. lignaria is much larger than either P. augusta or P. patrickensis, and there are significant differences in shell shape between the three taxa. Earlier mitochondrial DNA sequencing data, which supported specific status of P. augusta, is discussed. The snail's only habitat on the Mt Augustus ridgeline is described, but most has now been removed by coal mining. Snails salvaged before the destruction of their habitat have been taken into captivity or released in the wild outside their natural range.

Estimates of Population Size, Measurements of Sex Ratios, and Reported Mortality Rates for Bullsnakes (Pituophis catenifer sayi) at a Site in the Upper Midwestern United States

Abstract The characteristics of snake populations are reportedly difficult to quantify and such information exists for relatively few species, including Bullsnakes (Pituophis catenifer sayi). A Bullsnake population in southwestern Wisconsin was surveyed for three seasons (2003–05). All snakes encountered were (1) implanted with Passive Integrated Transponders for mark-recapture analyses of population size, (2) aged by size, and (3) sexed via probing and released. A subset of individuals was also implanted with radio transmitters to determine, in part, mortality rates and sources. Although recapture rates over the three years of surveying were low, an unbiased Lincoln-Petersen estimation was possible. This estimation revealed a small adult population size (N = 28.8) that was similar to the total number of adults encountered throughout the study (N = 30). Chi-squared analysis revealed that adult sex ratios were similar to 50 : 50 in all years. Mortality rates were high, particularly in females (44%), and so...

四国太平洋岸に共存するスナガニ属３種の季節的な分布パターンおよび食性

On sandy beaches of southern Shikoku, one temperate-zone crab, Ocypode stimpsoni, and two tropical and subtropical crabs, O. sinensis and O. ceratophthalma, co-occur, dwelling in individual burrows. Their distribution patterns, food habits, and physiological condition were investigated seasonally. Among the three species, O. sinensis was distributed in the highest zone vegetated with Vitex rotundifolia and Calystegia soldanella and was well segregated from the others except during its juvenile stage. It fed on terrestrial invertebrates and terrestrial plants. The distribution of O. ceratophthalma overlapped with that of O. stimpsoni; O. ceratophthalma mainly fed on terrestrial and aquatic invertebrates whereas O. stimpsoni fed on detritus and diatoms together with terrestrial and aquatic invertebrates. Ocypode ceratophthalma was poor in hepatopancreas index late in autumn and rarely overwintered, with the result that almost the entire population consisted of immature individuals. It is likely that the population of O. ceratophthalma in southern Shikoku is maintained by a supply of larvae from more southern regions. It is possible that O. stimpsoni, which is competitively inferior to O. ceratophthalma due to its smaller adult size, may become extinct in southern Shikoku if the recent rise in air temperature during winter enables more individuals of O. ceratophthalma to thrive there.

Ecological correlates of fish reproductive activity in floodplain rivers: a life-history-based approach

Reproductive activity of seven species representing three divergent life history strategies was monitored monthly for 2 years in channel and floodplain habitats of the Brazos River, Texas, USA, to evaluate associations between reproductive activity and biotic and abiotic factors predicted by conceptual models to influence reproduction. An information-theoretic approach was used to select best approximating models for each species, and model-averaged estimates of regression coefficients were calculated. Model selection indicated that monthly flow based on the 30-year hydrograph and temperature was strongly supported as factors associated with reproductive activity of all three life history strategies. The timing of reproduction in relation to the long-term hydrograph was related to life history traits. Reproductive activity of species with large adult size and high fecundity was greatest in spring just prior to increasing flows, whereas species with small adult size and extended breeding seasons exhibited greater activity in late spring and summer when mean flow was greatest. Nest-building species with parental care were more abundant in off-channel habitats where floods were less common. Instream flow management would benefit from consideration of flow and habitat requirements needed to support the diverse life history strategies displayed by fishes in river–floodplain systems.