Changes In Body Size Research Articles

Changes in prey body size differentially reduces predation risk across predator and prey abundances

Trophic interactions underpin the structure of ecological communities by describing the rates at which consumers exploit their resources. The rates at which predators consume their prey are influenced by prey traits, with many species inducing defensive modifications to prey traits following the threat of predation. Here we use different clonal lines of the protist Paramecium being consumed by Stenostomum predators to highlight how differences in prey traits impact rates of predation. Clonal lines differed in their body width traits, and in their ability to induce changes in body width. By using a factorial cross of predator and prey abundances for different clonal lines we demonstrate how evolutionary or induced alterations in prey traits can impact the relative threat of predation. Our experiments show how interference among predators impacts predation rate, and how increased body width increased predator handling times. Given that reductions in the strength of interspecific interactions are associated with increased levels of overall community stability, our results indicate how individual level changes may scale up to impact whole communities.

The development of dress forms in standing and sitting postures using 3D body scanning and printing

3D body scanning and printing are attracting attention as innovative technologies for producing dress forms. While designing dress forms, the shape of the human body must be accurately reflected in the different postures. This study explored the development of dress forms as a tool to understand changes in body size and shape according to postures and reflect this information to design and fit evaluation in the apparel industry. The holistic development process of dress forms in standing and sitting postures was suggested for representing the body shape of a specific target group. The average shape of middle-aged Korean women was derived by analyzing the 6th Size Korea data. A representative participant whose dimensions were closest to the average size was selected among recruited participants for the dress form development. The body data were acquired with a portable 3D scanner and corresponding dress forms and accessories were modeled using 3D CAD software. The models were inspected and corrected through prototyping. Full-size dress forms in standing and sitting postures were printed using a fused deposition modeling (FDM) 3D printer and post-processed. Completed dress forms were body-scanned and their accuracy was evaluated through morphological similarity comparison, cross-sectional image comparison, surface area and volume comparison, and mesh deviation analysis. Although there were some minor differences caused by the modeling process, the developed dress forms reflected the main characteristics and shapes of the representative body satisfactorily.

Species- and sex-dependent changes in body size between 1892 and 2017, and recent biochemical signatures in rural and urban populations of two ground beetle species.

Increasing urbanisation and intensified agriculture lead to rapid transitions of ecosystems. Species that persist throughout rapid transitions may respond to environmental changes across space and/or time, for instance by altering morphological and/or biochemical traits. We used natural history museum specimens, covering the Anthropocene epoch, to obtain long-term data combined with recent samples. We tested whether rural and urban populations of two ground beetle species, Harpalus affinis and H. rufipes, exhibit spatio-temporal intraspecific differences in body size. On a spatial scale, we tested signatures of nitrogen and carbon stable isotopes enrichments in different tissues and body components in recent populations of both species from urban and agricultural habitats. For body size examinations, we used beetles, collected from the early 20th century until 2017 in the Berlin-Brandenburg region, Germany, where urbanisation and agriculture have intensified throughout the last century. For stable isotope examinations, we used recent beetles from urban and agricultural habitats. Our results revealed no spatio-temporal changes in body size in both species' females. Body size of H. rufipes males decreased in the city but remained constant in rural areas over time. We discuss our findings with respect to habitat quality, urban heat and interspecific differences in activity pattern. Although nitrogen isotope ratios were mostly higher in specimens from agricultural habitats, some urban beetles reached equal enrichments. Carbon signatures of both species did not differ between habitats, detecting no differences in energy sources. Our results indicate that increasing urbanisation and intensified agriculture are influencing species' morphology and/or biochemistry. However, changes may be species- and sex-specific.

Exceptions to the temperature–size rule: no Lilliput Effect in end‐Permian ostracods (Crustacea) from Aras Valley (northwest Iran)

AbstractThe body size of marine ectotherms is often negatively correlated with ambient water temperature, as seen in many clades during the hyperthermal crisis of the end‐Permian mass extinction (c. 252 Ma). However, in the case of ostracods, size changes during ancient hyperthermal events are rarely quantified. In this study, we evaluate the body size changes of ostracods in the Aras Valley section (northwest Iran) in response to the drastic warming during the end‐Permian mass extinction at three taxonomic levels: class, order, species. At the assemblage level, the warming triggers a complete species turnover in the Aras Valley section, with larger, newly emerging species dominating the immediate post‐extinction assemblage for a short time. Individual ostracod species and instars do not show dwarfing or a change in body size as an adaptation to the temperature stress during the end‐Permian crisis. This may indicate that the ostracods in the Aras Valley section might have been exceptions to the temperature–size rule (TSR), using an adaptation mechanism that does not involve a decrease in body size. This adaptation might be similar to the accelerated development despite constant instar body sizes that can be observed in some recent experimental studies of ostracod responses to thermal stress.

Avian wings can lengthen rather than shorten in response to increased migratory predation danger.

Increasing predation danger can select for safety-enhancing modifications to prey morphology. Here, we document the multi-decade wing lengthening of a Pacific flyway migrant, the western sandpiper (Calidris mauri), and contrast this with contemporaneous wing shortening of the closely related semipalmated sandpiper (C. pusilla) on the Atlantic flyway. We measured >12,000 southbound western sandpipers captured from 1978 to 2020 at a major stopover site in British Columbia. Wing length increased at 0.074 mm year-1 (SE = 0.017; p < .0003) for adults, and 0.087 mm year-1 (SE = 0.029; p < .007) for juveniles. These rates are of similarly large magnitude (4%-5% overall), but opposite in direction, to the rate we previously reported for semipalmated sandpiper adults (-0.103 mm year-1). In both species, the change is specific to wings rather than being part of a general body size change. We interpret both trends as responses to the ongoing strong increase of peregrine falcon (Falco peregrinus) populations since the mid-1970s, an important predator encountered by these species in contrasting ways during migration. Western sandpipers and peregrine migrations have temporal and spatial overlap. Longer wings enhance migratory speed and efficiency, enabling western sandpipers to decrease overlap by advancing to safer zones ahead of falcon passage. In contrast, semipalmated sandpipers primarily encounter peregrines as residents at migratory staging sites. Shorter wings improve acceleration and agility, helping migrants to escape attacks. Juvenile western sandpiper wing length also shows a component additive to the lengthening trend, shifting between years at 0.055 mm day-1 with the highly variable snowmelt date, with wings shorter following early springs. On the Pacific flyway, the timing of peregrine southward passage advances with snowmelt, increasing the relative exposure of juveniles to post-migratory resident peregrines. We interpret this annual wing length adjustment as an induced defense, made possible because snowmelt timing is a reliable cue to danger in the upcoming migration.

Impact of COVID-19 confinement on food consumption pattern, physical activity and perceived body size of Nigerian undergraduates

Background and objectives: Unhealthy dietary practices and physical inactivity are major contributors to overweight and obesity which is fast becoming a public health concern among adolescents and young adults globally. This study aimed to investigate the impact of COVID-19 lockdown on food consumption pattern, physical activity and perceived body size changes of Nigerian undergraduates.&#x0D; Methods: This cross-sectional study used a snowball sampling technique to select 310 respondents. An online questionnaire link was forwarded to eligible respondents to elicit information on their dietary pattern, physical activity levels and perceived body size. Data collection for these indicators followed standard procedures and were compared with standard references.&#x0D; Results: The pattern of fruit, vegetable, legume, and meat/fish consumption significantly increased during the lockdown. Snack, soft-drink and dairy products experienced a decline in consumption (p &lt; 0.05). The physical activity MET (metabolic equivalent) score of respondents reduced from 3378.85 to 3097.02 MET minutes/week. Information on the perceived body size using body silhouette classification reported that lockdown accounted for an elevation in the perceived prevalence of overweight/obese (11.0% to 23.9%). &#x0D; Conclusion: COVID-19 confinement improved some dietary practices of the undergraduates, but significantly contributed to a decline physical activity levels and an elevation in perceived body size. Designing effective approaches such as home-made physical activity routines, and local food production may help avert such outcomes of restricted access to the external environment.

Parameterized shape adaptive materials for sportswear

PurposeConventional sportswear design does not take into account body size changes that many individuals experience (e.g. through pregnancy, puberty, menstruation, etc.). This paper aims to detail both the construction of a novel wearable shape-adaptive composite and a new meso-scale material design method, which enables the optimal creation of these structures.Design/methodology/approachThis work reports the development of a predictive computational model and a corresponding design tool, including results of a tensile testing protocol to validate their outputs. A mathematical model was developed to explore the geometric parameter space of a bi-stable composite system, which then feeds into an optimization design tool.FindingsThe authors found that it is possible to fabricate shape-adaptive composites via 3D printing bi-stable structures, and adhering them to a base textile. Experimental mechanical tensile testing showed good agreement with the predictive model in mid-range unit cell amplitude designs. To illustrate how the optimization design tool works this paper details two design examples, one for expected shape change during pregnancy and one for targeted compression for high performance swimwear. The optimized design parameters are shown to replicate the target parameters, however there is potential for further improvement with a lower stiffness base textile.Originality/valueAlthough there is a wealth of research on multi-stable mechanisms, there is a dearth of studies that apply these structures in the wearable composite space. Additionally, there is a need for design methods which leverage the structurally-programmable capabilities of multi-stable structures to create optimized, high-performance functional composites.

Effects of 2-Year Physical Activity and Dietary Intervention on Adrenarchal and Pubertal Development: The PANIC Study.

Childhood overweight has been linked to earlier development of adrenarche and puberty, but it remains unknown if lifestyle interventions influence sexual maturation in general populations. To investigate if a 2-year lifestyle intervention influences circulating androgen concentrations and sexual maturation in a general population of children. We conducted a 2-year physical activity and dietary intervention study in which 421 prepubertal and mostly normal-weight 6- to 9-year-old children were allocated either to a lifestyle intervention group (119 girls, 132 boys) or a control group (84 girls, 86 boys). The main outcome measures were serum dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulfate (DHEAS), androstenedione (A4), and testosterone concentrations, and clinical adrenarchal and pubertal signs. The intervention and control groups had no differences in body size and composition, clinical signs of androgen action, and serum androgens at baseline. The intervention attenuated the increase of DHEA (P = .032), DHEAS (P = .001), A4 (P = .003), and testosterone (P = .007) and delayed pubarche (P = .038) in boys but it only attenuated the increase of DHEA (P = .013) and DHEAS (P = .003) in girls. These effects of lifestyle intervention on androgens and the development of pubarche were independent of changes in body size and composition, but the effects of intervention on androgens were partly explained by changes in fasting serum insulin. A combined physical activity and dietary intervention attenuates the increase of serum androgen concentrations and sexual maturation in a general population of prepubertal and mostly normal-weight children, independently of changes in body size and composition.

Body size and weight status of adult Indian males born in the 1890s-1950s: Age and secular change in the context of demographic, economic, and political transformation.

To evaluate secular change in body size and weight status of adult Indian males born in 1891-1957 and surveyed in the 1970s. Data are from Anthropological Surveys. Only men were included in the surveys due to high female illiteracy and lack of female researchers. Indian society was also strongly conservative at the time, especially in rural areas, and the measurement of women by men was not permitted. Heights and weights of 43 950 males 18-84 years (born 1891-1957) were measured. The BMI was calculated; weight status of individuals was classified relative to WHO criteria and suggested criteria for the Asia-Pacific region. Heights of men 35+ years were also adjusted for age-related stature loss. Trends in measured and adjusted heights, body weight and the BMI, and in weight status were evaluated by age groups. Linear regression of measured height and adjusted height on year of birth was used to estimate secular effects. Mean heights declined slightly with age to 50 years and declined sharply through 60+ years, while mean weights increased into the 40s and then declined. Mean BMIs were relatively stable from 30 to 60 years. The prevalence of thinness and normal weight was high, while that of overweight and obesity was low. Regression analyses indicated limited secular change across the total range of birth years but suggested a decline in adjusted heights among men born in 1891 through the 1930s, and little change among men born subsequently. Age-related trends and results of the regression analyses by year of birth indicated negligible secular change in heights of Indian men 18-84 years born between 1891 and 1957. BMIs indicated a high prevalence of thinness and normal weight and low prevalence of overweight and obesity.

Investigating the Relationship between Growth Rate, Shell Morphology, and Trace Element Composition of the Pacific Littleneck Clam (Leukoma staminea): Implications for Paleoclimate Reconstructions

Due to their robust preservation and widespread nature, marine bivalve shells are increasingly used as informative, high-resolution records of past environmental conditions. Unfortunately, few studies have investigated variability amongst individuals in a genetic cohort and throughout their ontogeny. We measured several morphological properties and the element patterning of 200-day-old juvenile Leukoma staminea (Conrad, 1837) grown in identical conditions from the same reproductive cohort. We hypothesized that slower shell growth would correspond to the reduced incorporation of trace/minor elements (Sr, Mg, and S) in the aragonite lattice, as has been documented in other biomineralizing marine invertebrates. Microprobe analyses of adult shells revealed higher levels of S, Sr, and Mg in the dark, slower-growing growth lines compared to the light, faster-growing increments, particularly in the inner shell layer, thus refuting our hypothesis. Moreover, elemental count variation within single adult shells generally tracked changes in shell microstructure (i.e., higher counts in prismatic microstructures) and growth line patterns, and these differences are detectable on a micrometer scale. Juvenile shells of different sizes showed variation in S, Sr, and Mg counts as well, but it was unclear whether the variability closely tracked changes in microstructure, body size, and/or growth line patterns. In all individuals, regardless of life stage, the outermost shell layer showed higher Sr and S count values, and these elements closely mirrored each other within individual shells. The results presented herein represent the first in-depth description of the shell mineralogy, microstructure, body size variability, and geochemical properties of modern L. staminea, a common eastern Pacific, shallow, infaunal bivalve, allowing for the rigorous evaluation of L. staminea shells as recorders of past environmental and biological change. Significant intraspecific variation in the young body size, growth band patterning, and elemental composition of individuals of the same age and genetic stock complicates the use of size alone as a proxy for age in historical studies. Additionally, elemental composition shifted from high to low values (for example, Sr ranging from ~190 to 100 counts) at a very fine (micrometer) scale within single shells, as evidenced by visible correlations between microstructure and elemental composition. While young L. staminea shells are likely not useful as archives of (paleo)environmental conditions, adult L. staminea shells are likely suitable if micrometer-scale variability in shell structure and chemistry is accounted for.

Visual antipredator effects of web flexing in an orb web spider, with special reference to web decorations.

Some visual antipredator strategies involve the rapid movement of highly contrasting body patterns to frighten or confuse the predator. Bright body colouration, however, can also be detected by potential predators and used as a cue. Among spiders, Argiope spp. are usually brightly coloured but they are not a common item in the diet of araneophagic wasps. When disturbed, Argiope executes a web-flexing behaviour in which they move rapidly and may be perceived as if they move backwards and towards an observer in front of the web. We studied the mechanisms underlying web-flexing behaviour as a defensive strategy. Using multispectral images and high-speed videos with deep-learning-based tracking techniques, we evaluated body colouration, body pattern, and spider kinematics from the perspective of a potential wasp predator. We show that the spider's abdomen is conspicuous, with a disruptive colouration pattern. We found that the body outline of spiders with web decorations was harder to detect when compared to spiders without decorations. The abdomen was also the body part that moved fastest, and its motion was composed mainly of translational (vertical) vectors in the potential predator's optical flow. In addition, with high contrast colouration, the spider's movement might be perceived as a sudden change in body size (looming effect) as perceived by the predator. These effects alongside the other visual cues may confuse potential wasp predators by breaking the spider body outline and affecting the wasp's flight manoeuvre, thereby deterring the wasp from executing the final attack.

Variation and process of life history evolution in insular dwarfism as revealed by a natural experiment

Islands are a classic focus for evolutionary studies. One topic of great interest has been the evolution of “dwarfs,” significantly smaller island mammals relative to their continental counterparts. Although a consensus has been achieved regarding the multivariate ecological causes behind changes in body size, the processes involved remain largely unexplored. Life history variables, including age at first reproduction, growth rate, and longevity, are likely to be key to understanding the process of insular dwarfism. The Japanese archipelago, with its numerous islands, offers a unique natural experiment for the evolution of different sizes within the same group of organisms; namely, deer. Thus, we investigated eight deer populations with a total number of 52 individuals exhibiting body size variation, both extant and fossil, to clarify the effect of insularity on life history traits. We applied several methods to both extant and extinct populations to resolve life history changes among these deer populations. Skeletochronology, using lines of arrested growth formed in long bones (femur and tibia), successfully reconstructed body growth curves and revealed a gradual change in growth trajectories reflecting the degree of insularity. Slower growth rates with prolonged growth periods in more isolated deer populations were revealed. An extensive examination of bone microstructure further corroborated this finding, with much slower growth and later somatic maturity evident in fossil insular deer isolated for more than 1.5 Myr. Finally, mortality patterns assessed by demographic analysis revealed variation among deer populations, with a life history of insular populations shifting toward the “slow life.”

Ecological rules for global species distribution also predict performance variation in Ironman triathletes.

Bergmann's and Allen's rules predict changes in body size and appendage length across temperature gradients for species with broad geographic distributions. Larger bodies and longer limbs facilitate cooling whereas smaller bodies and compact limbs limit heat loss. Although these patterns are highly repeatable (hence "rules" of ecology) the patterns and underlying mechanisms are less-well understood in humans. Here I show that variation in running performance among human male triathletes is consistent with both Bergmann's and Allen's rules. Males (but not females) with relatively larger body size and longer limbs performed better at hot compared to cold race venues and vice-versa. Consistent with results in other taxa, sex-specificity may reflect selection for sexual dimorphism. Results suggest that ecological patterns detected over large-spatial scales may arise from fine-scale variation in locomotor performance.

Temperature-dependent Developmental Plasticity and Its Effects on Allen's and Bergmann's Rules in Endotherms.

Ecogeographical rules, describing common trends in animal form across space and time, have provided key insights into the primary factors driving species diversity on our planet. Among the most well-known ecogeographical rules are Bergmann's rule and Allen's rule, with each correlating ambient temperature to the size and shape of endotherms within a species. In recent years, these two rules have attracted renewed research attention, largely with the goal of understanding how they emerge (e.g., via natural selection or phenotypic plasticity) and, thus, whether they may emerge quickly enough to aid adaptations to a warming world. Yet despite this attention, the precise proximate and ultimate drivers of Bergmann's and Allen's rules remain unresolved. In this conceptual paper, we articulate novel and classic hypotheses for understanding whether and how plastic responses to developmental temperatures might contributed to each rule. Next, we compare over a century of empirical literature surrounding Bergmann's and Allen's rules against our hypotheses to uncover likely avenues by which developmental plasticity might drive temperature-phenotype correlations. Across birds and mammals, studies strongly support developmental plasticity as a driver of Bergmann's and Allen's rules, particularly with regards to Allen's rule. However, plastic contributions toward each rule appear largely non-linear and dependent upon: (1) efficiency of energy use (Bergmann's rule) and (2) thermal advantages (Allen's rule) at given ambient temperatures. These findings suggest that, among endotherms, rapid changes in body shape and size will continue to co-occur with our changing climate, but generalizing the direction of responses across populations is likely naive.

Associations of Change in Body Size With All-Cause and Cause-Specific Mortality Among Healthy Older Adults

The association between weight change and subsequent cause-specific mortality among older adults is not well described. The significance of changes in waist circumference (WC) has also not been compared with weight change for this purpose. To examine the associations of changes in body weight and WC with all-cause and cause-specific mortality. This cohort study is a post hoc analysis of data from the Aspirin in Reducing Events in the Elderly (ASPREE) randomized clinical trial, which recruited participants between March 1, 2010, and December 31, 2014. The study included community-based older adults (16 703 Australian participants aged ≥70 years and 2411 US participants aged ≥65 years) without evident cardiovascular disease (CVD), dementia, physical disability, or life-limiting chronic illness. Data analysis was performed from April to September 2022. Body weight and WC were measured at baseline and at annual visit 2. Analysis models were adjusted for baseline body mass index because height and weight were measured at baseline, allowing for calculation of body mass index and other variables. Both body weight and WC changes were categorized as change within 5% (stable), decrease by 5% to 10%, decrease by more than 10%, increase by 5% to 10%, and increase by more than 10%. All-cause, cancer-specific, CVD-specific, and noncancer non-CVD-specific mortality. Mortality events were adjudicated by an expert review panel. Cox proportional hazards regression and competing risk analyses were used to calculate hazard ratios (HRs) and 95% CIs. Among 16 523 participants (mean [SD] age, 75.0 [4.3] years; 9193 women [55.6%]), 1256 deaths were observed over a mean (SD) of 4.4 (1.7) years. Compared with men with stable weight, those with a 5% to 10% weight loss had a 33% higher (HR, 1.33; 95% CI, 1.07-1.66) risk of all-cause mortality, and those with more than a 10% decrease in body weight had a 289% higher (HR, 3.89; 95% CI, 2.93-5.18) risk. Compared with women with stable weight, those with a 5% to 10% weight loss had a 26% higher (HR, 1.26; 95% CI, 1.00-1.60) risk of all-cause mortality, and those with more than a 10% decrease in body weight had a 114% higher (HR, 2.14; 95% CI, 1.58-2.91) risk. Weight loss was associated with a higher cancer-specific mortality (>10% decrease among men: HR, 3.49; 95% CI, 2.26-5.40; 5%-10% decrease among women: HR, 1.44; 95% CI, 1.46-2.04; >10% decrease among women: HR, 2.78; 95% CI, 1.82-4.26), CVD-specific mortality (>10% decrease among men: HR, 3.14; 95% CI, 1.63-6.04; >10% decrease among women: HR, 1.92; 95% CI, 1.05-3.51), and noncancer non-CVD-specific mortality (>10% decrease among men: HR, 4.98; 95% CI, 3.14-7.91). A decrease in WC was also associated with mortality. This cohort study of healthy older adults suggests that weight loss was associated with an increase in all-cause and cause-specific mortality, including an increased risk of cancer, CVD, and other life-limiting conditions. Physicians should be aware of the significance of weight loss, especially among older men.

Differentially expressed genes associated with body size changes and transposable element insertions between Caenorhabditis elegans and its sister species, C. inopinata.

Why the recently discovered nematode Caenorhabditis inopinata differs so greatly from its sibling species Caenorhabditis elegans remains unknown. A previous study showed that C. inopinata has more transposable elements (TEs), sequences that replicate and move autonomously throughout the genome, potentially altering the expression of neighboring genes. In this study, we focused on how the body size of this species has evolved and whether TEs could affect the expression of genes related to species-specific traits such as body size. First, we compared gene expression levels between C. inopinata and C. elegans in the L4 larval and young adult stages-when growth rates differ most prominently between these species-to identify candidate genes contributing to their differences. The results showed that the expression levels of collagen genes were consistently higher in C. inopinata than in C. elegans and that some genes related to cell size were differentially expressed between the species. Then, we examined whether genes with TE insertions are differentially expressed between species. Indeed, the genes featuring C. inopinata-specific TE insertions had higher expression levels in C. inopinata than in C. elegans. These upregulated genes included those related to body size, suggesting that these genes could be candidates for artificial TE insertion to examine the role of TEs in the body size evolution of C. inopinata.

How scaling approaches can reveal fundamental principles in physiology and biomechanics

Among terrestrial mammals, the largest, the 3tonne African elephant, is one-million times heavier than the smallest, the 3g pygmy shrew. Body mass is the most obvious and arguably the most fundamental characteristic of an animal, impacting many important attributes of its life history and biology. Although evolution may guide animals to different sizes, shapes, energetic profiles or ecological niches, it is the laws of physics that limit biological processes and, in turn, affect how animals interact with their environment. Consideration of scaling helps us to understand why elephants are not merely scaled-up shrews, but rather have modified body proportions, posture and locomotor style to mitigate the consequences of their large size. Scaling offers a quantitative lens into how biological features vary compared with predictions based on physical laws. In this Review, we provide an introduction to scaling and its historical context, focusing on two fields that are strongly represented in experimental biology: physiology and biomechanics. We show how scaling has been used to explore metabolic energy use with changes in body size. We discuss the musculoskeletal and biomechanical adaptations that animals use to mitigate the consequences of size, and provide insights into the scaling of mechanical and energetic demands of animal locomotion. For each field, we discuss empirical measurements, fundamental scaling theories and the importance of considering phylogenetic relationships when performing scaling analyses. Finally, we provide forward-looking perspectives focused on improving our understanding of the diversity of form and function in relation to size.

Patterns and processes in the history of body size in turritelline gastropods, Jurassic to Recent

AbstractBody size is an important trait with implications for energy use and ecology as well as generation time and evolutionary rates. Turritelline gastropods are widely distributed through geologic time and space, making them an excellent group for evaluating macroevolutionary patterns. To evaluate the pattern of body-size change in turritelline gastropods, we compiled a dataset of shell lengths of 316 species of turritelline gastropods spanning the Jurassic to Recent. Type specimens were almost always significantly larger than specimen distributions from the same species. We found that turritelline gastropod size was inversely correlated with latitude, a trend likely driven by the Neogene–Recent diversification of small-bodied Southern Hemisphere taxa. A time series model was applied to distinguish among three possible macroevolutionary patterns: unbiased random walk (no directional trend), biased random walk (directional trend), and stasis (no net change). We determined that turritelline gastropods have experienced stasis in body size throughout their evolutionary history, adding to the growing literature documenting directionless body-size trends in marine invertebrate clades. Stasis of geographically widespread clades may be the result of ecological variability across the environmental range occupied by the group or differential diversification into opposing environments. Turritelline life-history patterns, especially their reproductive strategy that combines a short life span and decline in growth rate around 1 year of age to reallocate energy to reproduction, might circumvent selection for longevity and larger size, while further decrease in minimum size is likely limited by feeding efficiency and anti-predatory defense. The expectation that species or clades should continue to evolve to occupy larger size classes conflicts with the evolutionary advantages of small size, which in turritelline gastropods include high generational turnover and larger population sizes that yield opportunities for genetic variance.

Changes in body size in some bird species from the Yucatán peninsula since the Late Pleistocene

AbstractDuring the Pleistocene, the Yucatán Peninsula reached its greatest geographic extension, with 457,650 km2, but the rise of sea level after the Last Glacial Maximum (ca. 20,000–12,000 years ago) reduced its area to 225,182 km2(50.8% reduction). These geographic extension changes likely modified the extension of different habitats throughout the peninsula, which may have also promoted morphological changes in the species that inhabit this region. Here, we tested if the reduction of the geographic size of the Yucatán Peninsula may have promoted changes in the body size of three fossil bird species and two modern bird species. We compared Late Pleistocene bird fossils specimens from Loltún, Yucatán, Mexico (ca. 28,000–11,700 ya), San Josecito Cave and Tlapacoya, and study skins of collected specimens. To assess the area‐scale ratio and to establish if body size changes occurred over time from a large to a small body size, we relied on the “island rule” as a framework; we also relied on Bergmann's rule, which postulates a decreasing in size from north to south in homeothermic species to recognize if these birds show a north to south cline. Based on body mass and measurements of the tarsometatarsi, a reliable proxy for the estimation of body size, we performed statistical analyses to test for differences between fossil and non‐fossil birds, as well as to test a gradient in body mass north to south. We found a statistically significant trend in body size changes through time, from small body sizes in fossil birds to larger body sizes in non‐fossil birds. These results suggest that relatively recent ecological factors related to the environmental carrying capacity may have promoted body size variations in birds from the Yucatán Peninsula. We also found that modern population of bird species follow Bergmann's rule.

Fecundity trends of Chinook salmon in the Pacific Northwest

AbstractFecundity is an important demographic parameter that contributes to the productivity of anadromous fish stock dynamics. Yet, studies on fecundity patterns in Pacific salmon (Oncorhynchusspp.) often only include a few years of data, limiting our ability to understand spatio‐temporal trends. Here, we used data on 43 hatchery Chinook salmon (O. tshawytscha, Salmonidae) populations in Washington State to evaluate whether average fecundity changed over the past three decades. We then used data from a subset of stocks (18) to evaluate the relationship between fecundity and body length. Our results revealed significant changes in fecundity across the 25‐year study period with most stocks showing declines in fecundity over the past decade. Results further showed that Chinook salmon have decreased in length over this same period and that annual variation in mean length explains a majority (62%) of annual variation in mean fecundity. Specifically, we estimated that a 1‐mm reduction in length results in 7.8 fewer eggs (95% CI = 6.6–8.9). Given that the majority of Pacific Northwest Chinook salmon in the environment and harvested in fisheries originate from hatchery releases and that nearby hatchery and wild populations generally have similar ocean distributions, these results likely reflect patterns for many populations not included. Combined, our results highlight the need to consider changes in body size and egg production when assessing the dynamics of anadromous fish populations and designing management or conservation plans, particularly for depressed populations.