Small Body Size Research Articles

Directional selection, not the direction of selection, affects telomere length and copy number at ribosomal RNA loci

Many fisheries exert directional selection on traits such as body size and growth rate. Whether directional selection impacts regions of the genome associated with traits related to growth is unknown. To address this issue, we characterised copy number variation in three regions of the genome associated with cell division, (1) telomeric DNA, (2) loci transcribed as ribosomal RNA (rDNA), and (3) mitochondrial DNA (mtDNA), in three selection lines of zebrafish reared at three temperatures (22 °C, 28 °C, and 34 °C). Selection lines differed in (1) the direction of selection (two lines experienced directional selection for large or small body size) and (2) whether they experienced any directional selection itself. Lines that had experienced directional selection were smaller, had lower growth rate, shorter telomeres, and lower rDNA copy number than the line that experiencing no directional selection. Neither telomere length nor rDNA copy number were affected by temperature. In contrast, mtDNA content increased at elevated temperature but did not differ among selection lines. Though directional selection impacts rDNA and telomere length, direction of such selection did not matter, whereas mtDNA acts as a stress marker for temperature. Future work should examine the consequences of these genomic changes in natural fish stocks.

Small body size is associated with increased evolutionary lability of wing skeleton proportions in birds

Birds are represented by 11,000 species and a great variety of body masses. Modular organisation of trait evolution across birds has facilitated simultaneous adaptation of different body regions to divergent ecological requirements. However, the role modularity has played in avian body size evolution, especially small-bodied, rapidly evolving and diverse avian subclades, such as hummingbirds and songbirds, is unknown. Modularity is influenced by the intersection of biomechanical restrictions, adaptation, and developmental controls, making it difficult to uncover the contributions of single factors such as body mass to skeletal organisation. We develop a novel framework to decompose this complexity, assessing factors underlying the modularity of skeletal proportions in fore-limb propelled birds distributed across a range of body masses. We demonstrate that differences in body size across birds triggers a modular reorganisation of flight apparatus proportions consistent with biomechanical expectations. We suggest weakened integration within the wing facilitates radiation in small birds. Our framework is generalisable to other groups and has the capacity to untangle the multi-layered complexity intrinsic to modular evolution.

A new species of the endemic Tarsomys clade (Muridae, Rodentia) from eastern Mindanao Island, Philippines

Abstract Based on molecular and morphological evidence, we describe a new species of murine rodent from Mt. Kampalili in easternmost Mindanao Island, Philippines. It is the third known species of Tarsomys, a genus endemic to Mindanao. The new species differs from congeners (T. apoensis and T. echinatus) in having smaller body size, shorter tail, smaller hind feet, soft and dense pelage of darker color, smaller skull with a broader zygomatic plate, shorter incisive foramina, and longer auditory bullae. The new species belongs to the “Tarsomys clade” of tribe Rattini that has diversified principally on Mindanao where, in addition to the 3 species of Tarsomys, it is represented by 2 species of Limnomys and 1 species of Baletemys. The Tarsomys clade also includes the Rattus everetti complex which is widespread throughout the oceanic portion of the Philippines and likely consists of at least 4 species. Molecular phylogenetic analysis strongly supports a sister relationship between this new species and T. apoensis, which diverged approximately 1.0 to 1.75 Ma. The phylogenetic position, morphological distinctness, and relatively ancient persistence of this species support within-island diversification as the most substantial contributor to existing species richness of small mammals in the Philippines.

Female proportion has a stronger influence on dispersal than body size in nematodes of mountain lakes.

Nematodes disperse passively and are amongst the smallest invertebrates on Earth. Free-living nematodes in mountain lakes are highly tolerant of environmental variations and are thus excellent model organisms in dispersal studies, since species-environment relationships are unlikely to interfere. In this study, we investigated how population or organism traits influence the stochastic physical nature of passive dispersal in a topologically complex environment. Specifically, we analyzed the influence of female proportion and body size on the geographical distribution of nematode species in the mountain lakes of the Pyrenees. We hypothesized that dispersal is facilitated by (i) a smaller body size, which would increase the rate of wind transport, and (ii) a higher female proportion within a population, which could increase colonization success because many nematode species are capable of parthenogenetic reproduction. The results showed that nematode species with a low proportion of females tend to have clustered spatial distributions that are not associated with patchy environmental conditions, suggesting greater barriers to dispersal. When all species were pooled, the overall proportion of females tended to increase at the highest elevations, where dispersal between lakes is arguably more difficult. The influence of body size was barely relevant for nematode distributions. Our study highlights the relevance of female proportion as a mechanism that enhances the dispersal success of parthenogenetic species, and that female sex is a determining factor in metacommunity connectivity.

Impact of Maternal Exercise on Mice Offspring Development, Pulmonary Hypertension, and Vascular Remodeling in Chronic Hypoxia.

Chronic, high-altitude hypoxic exposure increases the risk of high-altitude pulmonary hypertension (PH). Emerging evidence shows maternal exercise may improve offspring resistance to disease throughout life. The purpose of this study is to determine if maternal exercise mitigates chronic hypoxic-induced changes in the offspring indicative of high-altitude PH development. Female adult C57BL/6J mice were randomly allocated to nonexercise or exercise conditions. Exercise consisted of voluntary running wheel exercise for 4 wk during the perinatal period. Three days after birth, the pups remained at low altitude (normoxia) or were exposed to hypobaric hypoxia of 450 mm Hg to simulate ~4500 m of altitude exposure until 8 wk of age. The study consisted of four groups: hypoxia + nonexercise pregnancy, hypoxia + exercise, or the respective normoxia conditions (normoxia + nonexercise or normoxia + exercise). Offspring body size, motor function, right ventricular systolic pressure (RVSP), and cardiopulmonary morphology were assessed after 8 wk in normoxia or hypoxia. Both hypoxic groups had smaller body sizes, reduced motor function, increased hematocrit, RVSP, muscularization in medium-sized pulmonary arteries, as well as right ventricular hypertrophy and contractility compared with the normoxic groups ( P < 0.05). Chronic hypoxia simulating 4500 m attenuated growth, lowered motor function, and elicited PH development. Voluntary maternal exercise did not significantly decrease RVSP in the offspring, which aligned with a lack of effect to attenuate abnormal body size and cardiopulmonary development due to chronic hypoxia. These findings are preliminary in nature, and more powered studies through larger group sizes are required to generalize the results to the population.

Physiology Evolves Convergently but Lags Behind Warming inCities.

Cities, through the generation of urban heat islands, provide a venue for exploring contemporary convergent evolution to climatic warming. We quantified how repeatable the evolution of heat tolerance, cold tolerance, and body size was among diverse lineages in response to urban heat islands. Our study revealed significant shifts toward higher heat tolerance and diminished cold tolerance among urban populations. We further found that the magnitude of trait divergence was significantly and positively associated with the magnitude of the urban heat island, suggesting that temperature played a major role in the observed divergence in thermal tolerance. Despite these trends, the magnitude of trait responses lagged behind environmental warming. Heat tolerance responses exhibited a deficit of 0.84°C for every 1°C increase in warming, suggesting limits on adaptive evolution and consequent adaptational lags. Other moderators were predictive of greater divergence in heat tolerance, including lower baseline tolerance and greater divergence in body size. Although terrestrial species did not exhibit systematic shifts toward larger or smaller body size, aquatic species exhibited significant shifts toward smaller body size in urban habitats. Our study demonstrates how cities can be used to address long-standing questions in evolutionary biology regarding the repeatability of evolution. Importantly, this work also shows how cities can be used as forecasting tools by quantifying adaptational lags and by developing trait-based associations with responses to contemporary warming.

Small skeletons show size-specific scaling: an exploration of allometry in the mammalian lumbar spine.

Studies of vertebrate bone biomechanics often focus on skeletal adaptations at upper extremes of body mass, disregarding the importance of skeletal adaptations at lower extremes. Yet mammals are ancestrally small and most modern species have masses under 5 kg, so the evolution of morphology and function at small size should be prioritized for understanding how mammals subsist. We examined allometric scaling of lumbar vertebrae in the small-bodied Philippine endemic rodents known as cloud rats, which vary in mass across two orders of magnitude (15.5 g-2700 g). External vertebral dimensions scale with isometry or positive allometry, likely relating to body size and nuances in quadrupedal posture. In contrast to most mammalian trabecular bone studies, bone volume fraction and trabecular thickness scale with positive allometry and isometry, respectively. It is physiologically impossible for these trends to continue to the upper extremes of mammalian body size, and we demonstrate a fundamental difference in trabecular bone allometry between large- and small-bodied mammals. These findings have important implications for the biomechanical capabilities of mammalian bone at small body size; for the selective pressures that govern skeletal evolution in small mammals; and for the way we define 'small' and 'large' in the context of vertebrate skeletons.

The thermoneutral zone in women takes an “arctic” shift compared to men

Conventionally, women are perceived to feel colder than men, but controlled comparisons are sparse. We measured the response of healthy, lean, young women and men to a range of ambient temperatures typical of the daily environment (17 to 31 °C). The Scholander model of thermoregulation defines the lower critical temperature as threshold of the thermoneutral zone, below which additional heat production is required to defend core body temperature. This parameter can be used to characterize the thermoregulatory phenotypes of endotherms on a spectrum from "arctic" to "tropical." We found that women had a cooler lower critical temperature (mean ± SD: 21.9 ± 1.3 °C vs. 22.9 ± 1.2 °C, P = 0.047), resembling an "arctic" shift compared to men. The more arctic profile of women was predominantly driven by higher insulation associated with more body fat compared to men, countering the lower basal metabolic rate associated with their smaller body size, which typically favors a "tropical" shift. We did not detect sex-based differences in secondary measures of thermoregulation including brown adipose tissue glucose uptake, muscle electrical activity, skin temperatures, cold-induced thermogenesis, or self-reported thermal comfort. In conclusion, the principal contributors to individual differences in human thermoregulation are physical attributes, including body size and composition, which may be partly mediated by sex.

Whole-Genome Sequencing Analyses Reveal the Evolution Mechanisms of Typical Biological Features of Decapterus maruadsi.

Decapterus maruadsi is a typical representative of small pelagic fish characterized by fast growth rate, small body size, and high fecundity. It is a high-quality marine commercial fish with high nutritional value. However, the underlying genetics and genomics research focused on D. maruadsi is not comprehensive. Herein, a high-quality chromosome-level genome of a male D. maruadsi was assembled. The assembled genome length was 716.13 Mb with contig N50 of 19.70 Mb. Notably, we successfully anchored 95.73% contig sequences into 23 chromosomes with a total length of 685.54 Mb and a scaffold N50 of 30.77 Mb. A total of 22,716 protein-coding genes, 274.90 Mb repeat sequences, and 10,060 ncRNAs were predicted, among which 22,037 (97%) genes were successfully functionally annotated. The comparative genome analysis identified 459 unique, 73 expanded, and 52 contracted gene families. Moreover, 2804 genes were identified as candidates for positive selection, of which some that were related to the growth and development of bone, muscle, cardioid, and ovaries, such as some members of the TGF-β superfamily, were likely involved in the evolution of typical biological features in D. maruadsi. The study provides an accurate and complete chromosome-level reference genome for further genetic conservation, genomic-assisted breeding, and adaptive evolution research for D. maruadsi.

Stable isotope analysis provides novel insights for measuring lake ecosystem recovery following acidification

Unstable and simplified freshwater food webs impair the resilience of Canadian fisheries facing environmental stressors. This study utilizes stable isotope analyses to assess trophic recovery to explore food web resiliency in lakes historically impacted by metal mining in Sudbury, Ontario. Carbon (δ13C) and nitrogen (δ15N) stable isotope ratios were quantified in yellow perch ( Perca flavescens), smallmouth bass ( Micropterus dolomieu), and baseline organisms to develop quantitative population metrics and describe dietary niche partitioning. The most severely damaged lake with a barren watershed had the lowest trophic positioning, smallest body size and niche area, and greatest niche overlap among fish species. Semi-barren and forested watershed lakes were more similar to reference lakes in isotopic metrics; however, elevated niche overlap and reduced trophic positioning suggests recovery in these lakes is ongoing. We found that including stable isotope analyses in lake recovery studies provided critical insights not captured by traditional biomonitoring approaches.

Effects of plant taxonomic position on soil nematode communities in Antarctica.

Antarctica terrestrial ecosystems are facing the most threats from global climate change, which is altering plant composition greatly. These transformations may cause major reshuffling of soil community composition, including functional traits and diversity, and therefore affect ecosystem processes in Antarctica. We used high-throughput sequencing analysis to investigate soil nematodes under 3 dominant plant functional groups (lichens, mosses, and vascular plants) and bare ground in the Antarctic region. We calculated functional diversity of nematodes based on their diet, life histories, and body mass with kernel density n-dimensional hypervolumes. We also calculated taxonomic and functional beta diversity of the nematode communities based on Jaccard dissimilarity. The presence of plants had no significant effect on the taxonomic richness of nematodes but significantly increased nematode functional richness. The presence of plants also significantly decreased taxonomic beta diversity (homogenization). Only mosses and vascular plants decreased nematode functional beta diversity, which was mostly due to a decreased effect of the richness difference component. The presence of plants also increased the effect of deterministic processes potentially because environmental filtering created conditions favorable to nematodes at low trophic levels with short life histories and small body size. Increasing plant cover in the Antarctic due to climate change may lead to increased diversity of nematode species that can use the scarce resources and nematode taxonomic and functional homogenization. In a future under climate change, community restructuring in the region is possible.

Interaction of left ventricular size with the outcome of cardiac resynchronization therapy in Japanese patients.

We analyzed the influence of the QRS duration (QRSd) to LV end-diastolic volume (LVEDV) ratio on cardiac resynchronization therapy (CRT) outcomes in heart failure patients classified as III/IV per the New York Heart Association (NYHA) and with small body size. We proposed the hypothesis that the QRSd/LV size ratio is a better index of the CRT substrate. We enrolled 114 patients with advanced heart failure (NYHA class III/IV, and LV ejection fraction >35%) who received a CRT device, including those with left bundle branch block (LBBB) and QRSd ≥120 milliseconds (n = 60), non-LBBB and QRSd ≥150 milliseconds (n = 30) and non-LBBB and QRSd of 120-149 milliseconds (n = 24). Over a mean follow-up period of 65 ± 58 months, the incidence of the primary endpoint, a composite of all-cause death and hospitalization for heart failure, showed no significant intergroup difference (43.3% vs. 50.0% vs. 37.5%, respectively, p = .72). Similarly, among 104 patients with QRSd/LVEDV ≥ 0.67 (n = 54) and QRSd/LVEDV < 0.67 (n = 52), no significant differences were observed in the incidence of the primary endpoint (35.1% vs. 51.9%, p = .49). Nevertheless, patients with QRSd/LVEDV ≥ 0.67 showed better survival than those with QRSd/LVEDV < 0.67 (14.8% vs. 34.6%, p = .0024). Advanced HF patients with a higher QRSd/LVEDV ratio showed better survival in this small-body-size population. Thus, the risk is concentrated among those with a larger QRSd, and patients with a relatively smaller left ventricular size appeared to benefit from CRT.

Почвенная нематода Caenorhabditis elegans как модель для изучения паразитических нематод

The free-living soil nematode Caenorhabditis elegans has been used as model organism in biological researches since middle of the 1960th. The short lifecycle, small body size, high fecundity, simplicity and cheapness of cultivation in laboratory, and safety for researchers are advantages of C. elegans as experimental model to study biology of Metazoa. The discussion about the possibility to use C. elegans as the model for parasitic nematodes started with the first mention of this nematode in scientific literature. The present article is the review of experimental studies demonstrating that in many cases substances toxic for C. elegans are also toxic for parasitic nematodes, and vice versa. This allows making a conclusion about the prospectivity to use C. elegans for initial screening for substances with nematicidal activity followed by their testing in experiments with parasitic nematodes. The possibility to use C. elegans for understanding mechanisms of nematicides action is also indisputable. On the whole one may conclude that C. elegans is a useful model both for searching new substances with anthelmintic activity and solution of the problem to overcome drug resistance of helmints.

Simulated reproductive allocation to fisheries-induced evolution among small yellow croaker populations in the Yellow and Bohai Seas

Fishery-induced evolution (FIE) affects the body size and reproduction of offspring, resulting in feedback regulation of fish survival and stock recruitment. Small yellow croaker (Larimichthys polyactis) is a species of high ecological and commercial importance in the Yellow and Bohai Seas, with large fluctuations in abundance linked to overfishing and environmental changes in recent decades. To better understand the maturation size and age, threshold reproduction cost, and energy trade-offs of small yellow croaker under environmental changes (e.g. conditions) and human impacts (e.g. fishing) in the Yellow and Bohai Seas, we utilised a two-pool uncertain growth model containing the growth threshold of reproductive energy and reproductive energy cost. The results showed that for growth, maturation age, and reproduction under the baseline scenario based on field survey data from the 1950 s, when resources for small yellow croaker were underexploited, the average age was 5–6 years old and the average body length was approximately 220 mm. As the model parameters for fishing pressure and condition mortality increased, small yellow croaker tended to mature earlier, had a smaller body size, and allocated more energy to reproduction, resulting in higher population fecundity but shorter lifespan. Higher reproductive costs led to a greater proportion of reproductive energy being allocated during the spawning period, resulting in an older age of sexual maturity, shorter lifespan for spawning populations, and poor physical conditions, resulting in higher post-reproductive mortality and a limited capacity for stock recruitment. The key life-history traits of small yellow croaker, including maturity age, mean age of the population, age-specific body weight, and spawn production at different age stages, can change under different conditions. The model represents the main life history strategies and energy allocation characteristics of small yellow croaker. The simulated age and body size were within the observed range and the predicted fecundity aligned with the observed values. This study provides a prediction tool for protecting the spawning and recruitment of small yellow croaker and establishes a biological reference for sustainable management of small yellow croaker populations in the Yellow and Bohai Seas in the future.

Can cyclone exposure explain behavioural and demographic variation among lemur species?

Madagascar has a harsh and stochastic climate because of regular natural disturbances. This history of regular cyclones has been hypothesised to have directed evolutionary changes to lemur behaviour and morphology that make them more resilient to sudden environmental change. These adaptations may include: small group sizes, high degrees of energy-conserving behaviours, generalist habitat use, small home ranges, small body size, and a limited number of frugivorous species. To date, however, no one has tested how variation in cyclone exposure across Madagascar is associated with variation in these resilience traits. In this study, we created a detailed cyclone impact map for Madagascar using Koppen-Geiger climate class, historical cyclone tracks, the Saffir Class of cyclone and hurricane intensity, and precipitation data. We also used existing literature to calculate a resilience score for 26 lemur species for which data existed on resilience traits. Our cyclone impact map was then overlaid on known geographic ranges of these species and compared to resilience score while controlling for phylogenetic non-independence and spatial autocorrelation. We found no association between cyclone impact in a lemur range and their resilience score. When assessing traits individually, however, we found that cyclone impact was positively associated with body size, suggesting that the more impacted a species is by cyclones the smaller they are. We also found cyclone impact to be negatively associated with frugivory, with species in higher impact zones eating more fruit. While unexpected, this could reflect an increased production in fruit in tree fall gaps following cyclones. While we did not find a pattern between cyclone impact and behavioural resilience in lemurs, we suggest a similar study at a global scale across all primates would allow for more taxonomic variation and reveal larger patterns key to understanding past and future vulnerability to natural disturbances in primates.

Two new species of the Cnemaspisgalaxia complex (Squamata, Gekkonidae) from the eastern slopes of the southern Western Ghats.

Two new species allied to Cnemaspisgalaxia are described from the eastern slopes of the south Western Ghats, Tamil Nadu, India. Both new species are members of the ornata subclade within the beddomei clade. The two new species can be easily distinguished from all other members of the beddomei clade and each other by a combination of nonoverlapping morphological characters such as small body size, distinct colouration of both sexes, the number of dorsal tubercles around the body, the number or arrangement of paravertebral tubercles, the number of midventral scales across the belly and longitudinal ventral scales from mental to cloaca, besides uncorrected pairwise ND2 and 16S sequence divergence of ≥ 7.4% and ≥ 2.7%. The two new species are distributed from low elevation, deciduous forests of Srivilliputhur, and add to the five previously known endemic vertebrates from Srivilliputhur-Megamalai Tiger Reserve.

NUS1 Variants Cause Lennox-Gastaut Syndrome Related to Unfolded Protein Reaction Activation.

NUS1 encodes the Nogo-B receptor, a critical regulator for unfolded protein reaction (UPR) signaling. Although several loss-of-function variants of NUS1 have been identified in patients with developmental and epileptic encephalopathy (DEE), the role of the NUS1 variant in Lennox-Gastaut syndrome (LGS), a severe child-onset DEE, remains unknown. In this study, we identified two de novo variants of NUS1, a missense variant (c.868C > T/p.R290C) and a splice site variant (c.792-2A > G), in two unrelated LGS patients using trio-based whole-exome sequencing performed in a cohort of 165 LGS patients. Both variants were absent in the gnomAD population and showed a significantly higher observed number of variants than expected genome-wide. The R290C variant was predicted to damage NUS1 and decrease its protein stability. The c.792-2A > G variant caused premature termination of the protein. Knockdown of NUS1 activated the UPR pathway, resulting in apoptosis of HEK293T cells. Supplementing cells with expression of wild-type NUS1, but not the mutant (R290C), rescued UPR activation and apoptosis in NUS1 knockdown cells. Compared to wild-type Drosophila, seizure-like behaviors and excitability in projection neurons were significantly increased in Tango14 (homolog of human NUS1) knockdown and Tango14R290C/+ knock-in Drosophila. Additionally, abnormal development and a small body size were observed in both mutants. Activated UPR signaling was also detected in both mutants. Thus, NUS1 is a causative gene for LGS with dominant inheritance. The pathogenicity of these variants is related to the UPR signaling activation, which may be a common pathogenic mechanism of DEE.

Decadal changes of macrofauna community in a semi-enclosed Bay of Yueqing in East China Sea

To reveal the long-term variation of macrofauna community in Yueqing Bay, an aquacultural bay famous for its shellfish culturing in the East China Sea, macrofauna samples were collected in three period from 2002 to 2003 and 2006–2007 to 2020–2021. The results show that macrofaunal community structure in this area has changed significantly (ANOSIM, p < 0.01) in nearly two decades with significant decreases in species number, biodiversity index and average biomass. Meanwhile, the taxa composition also changed significantly as the dominance of annelid increased while that of mollusks, echinoderms and vertebrates decreased. As a consequence of the variation of taxa composition and total biomass, macrofauna community showed a tendency of miniaturization as individuals with smaller body size and lower biomass dominated the community. According to the results of CCA analysis, temperature, salinity and dissolved oxygen content were the main environmental factors that restricted the species composition of macrofauna community. Further studies still needed to reveal the main reasons that cause the variation of macrofauna community. Overall, the results of this study suggest that the present status of Yueqing Bay benthic ecosystem is concerning from a macrobenthos perspective, as the biodiversity index and biomass of macrofauna decreased significantly. Effective measures should be taken in urgently to restrain the safety and function of coastal ecosystems.

A new species of Eocene fossil Malthodes (Coleoptera: Cantharidae) with a rarely observed aedeagus.

A new Malthodes (Coleoptera, Cantharidae, Malthininae) in Eocene amber from Poland (Baltic amber) is illustrated and described here: Malthodes (s. str.) maximiliani sp. nov. The new species of soldier beetle is characterized by its small body size and last tergites and last sternite distinct from similar taxa. Notably, the specimen has a partially visible aedeagus, a characteristic rarely seen in fossil Malthodes of the nominotypical subgenus; it has been observed in only three fossil species of this subgenus.

The first fossil of a tenebrionoid taxonomic enigma: Agnathus Germar (Coleoptera: Pyrochroidae: Agnathinae) in Bitterfeld amber, with remarks about age and geographic origin of the fossil

ABSTRACT Based on an inclusion in Bitterfeld amber, the first extinct species of the subfamily Agnathinae (Pyrochroidae) is described and illustrated. Agnathus groehni sp. nov. differs from two extant congeners in having the smaller body size; transverse W-shaped groove near posterior pronotal margin; the unicolourous black body and the elytral pubescence uniform without tomentose pattern. As demonstrated herein, the genus Agnathus is morphologically stable over at least 23 Ma years and inhabited the Western Palaearctic already in the Palaeogene. Zoogeography of extant species, palaeobionomy of the extinct species and difficulties in its reconstruction, as well as age and origin of Bitterfeld amber, are briefly discussed.