Head Length Research Articles

Association of polymorphism in the promotor area of the caprine BMPR1B gene with litter size and body measurement traits in Damani goats.

This study aimed to explore polymorphisms in the promoter region of the caprine BMPR1B (Bone morphogenetic protein receptor 1 beta) gene and its association with body measurement and litter size traits in Damani does. A total of 53 blood samples were collected to analyze the association between the BMPR1B gene polymorphism and 11 phenotypic traits in Damani female goats. The results revealed that three novel SNPs were identified in the promoter region of the caprine BMPR1B gene, including g.67 A > C (SNP1), g.170 G > A(SNP2), and g.501A > T (SNP3), among which the SNP1 and SNP2 were significantly (p < 0.05) associated with litter size and body measurement traits in Damani goats. In SNP1 the AC genotype could be used as a marker for litter size, and the CC genotype for body weight in Damani goats. In SNP2, the genotype GG was significantly (p < 0.05) associated with ear and head length. Therefore, we can conclude from the present study, that genetic variants AC and CC of the caprine BMPR1B gene could be used as genetic markers for economic traits through marker-assisted selection for the breed improvement program of the Damani goat.

An integrative taxonomic study on needlefishes (Belonidae) unveils two new species within the genus Ablennes from the Indian Ocean

The needlefish genus Ablennes remains monotypic, characterized by the globally distributed flat needlefish known as Ablennes hians. Their taxonomy has been mired with ambiguities due to the greater-than-average morphological variations observed in samples from different regions. Utilizing integrated taxonomic methods relying on mitochondrial molecular markers, it was revealed that the species initially perceived as a single entity is, in fact, a complex comprising at least three different species. In this context, we introduce two new species: Ablennes joseberchmansis sp. nov. and Ablennes gracalii sp. nov., They are morphologically distinct: in view of the morphometry and meristic characteristics. A. joseberchmansis sp. nov. and A. gracalii sp. nov. display distinct differentiation characteristics from A. hians in terms of dorsal fin, nostril position, dorsal fin origin, vertebrae count, scale counts, head length, eye diameter, interorbital width, maxilla length, dorsal ray height, depth at pelvic origin, lower lobe of the caudal fin, and caudal peduncle depthcaudal peduncle depth. These variations highlight their unique morphological traits and aid in their differentiation within the genus Ablennes. We assessed genetic relationships using a Maximum likelihood (ML) phylogenetic tree, revealing three distinct clades of morphological differences in Ablennes specimens from different morphological groups. The genetic variation, as represented by Kimura 2 parameter (K2P) distances, within the three Ablennes species spans from 6.5% to 9.4%. More specifically, we observed a 7.5% genetic difference between A. hians and A. joseberchmansis sp. nov., and a 6.5% distinction between A. hians and A. gracalii sp. nov. The interspecies divergence between the two newly identified species measured at 9.4%. These findings, which showcase the genetic distinctions among the three morphologically distinct Ablennes specimens, provide strong confirmation for the existence of three separate species within the Ablennes genus of needlefish in the Indian Ocean.

Morphological characterization and the relationship between morphometric indices of a local Cyprus fat–tailed Sheep breed in Cyprus

With many local breeds in danger of extinction or genetic erosion, the loss of genetic variety in farm animal genetic resources is an increasingly critical concern. Conserving diverse sheep breeds is crucial for long–term agricultural sustainability and ecosystem health. The current research focused on the Cyprus fat–tailed sheep, which is important for both meat and milk production, particularly to produce Halloumi cheese. A study on a Cyprus sheep production farm was carried out with the aim to characterize the morphological traits of Cyprus fat–tailed sheep breed for its conservation. The study found that in female Cyprus fat–tailed sheep, white, white–black, and brown coat color patterns were the common ones recorded with proportions of 75, 12.5, and 12.5%, respectively. Sixty seven percent of males were white–black followed by white coat color in 33%. Male sheep are all characterized by white fleece, while females had a range of fleece colors with the majority in white (75%) followed by pale greyish brown in 18.75% and fawn fleece in 6.25%. On the other hand, male Cyprus fat–tailed sheep had higher values (P&lt;0.05) for wither height, heart girth, chest width, hip height, foreleg length, compact index, area index, and body weight than females. Morphometric traits, such as head length, wither height, heart girth, chest depth, body length, and hip height, were significantly positively (P&lt;0.01) correlated with body weight. The study concludes that the characterization of the Cyprus fat–tailed sheep breed’s physical and morphological traits is essential and useful for its conservation.

Electron Microscopic and Morphometric Analysis of Wistar Rat Sperm

The aim of the study is to image and morphologically examine epididymal sperm in Wistar rats with scanning electron microscopy (SEM). The material of the study was epididymal sperm taken from three Wistar Rats. Routine fixation was performed on the obtained epididymal sperm using 2.5% glutaraldehyde solution. Morphometric measurements of sperm were carried out using scanning electron microscopy. The study focused on examining various regions of the sperm, including the head, midpiece, and the remainder of the flagellar segment. Measurements were taken into account in semen that preserved its integrity in different fields. Measurements of these regions were made with the ImageJ program. As a result of the measurements, it was determined that the average head length of rat semen was 7.821 ± 0.844 μm, the average total flagellum length was 168.549 ± 9.19 μm and the average flagellum/head ratio was 21.550 and the flagellum was quite long. It was observed that the measurements of the rat sperm used in the study were consistent with the measurements of other rat sperm. When the studies were examined, it was concluded that rat sperm has an extremely long flagellum compared to its body size. The morphological differences of the sperms revealed will be a guide for experimental studies.

Aspartame Causes Developmental Defects and Teratogenicity in Zebra Fish Embryo: Role of Impaired SIRT1/FOXO3a Axis in Neuron Cells.

Aspartame, a widely used artificial sweetener, is present in many food products and beverages worldwide. It has been linked to potential neurotoxicity and developmental defects. However, its teratogenic effect on embryonic development and the underlying potential mechanisms need to be elucidated. We investigated the concentration- and time-dependent effects of aspartame on zebrafish development and teratogenicity. We focused on the role of sirtuin 1 (SIRT1) and Forkhead-box transcription factor (FOXO), two proteins that play key roles in neurodevelopment. It was found that aspartame exposure reduced the formation of larvae and the development of cartilage in zebrafish. It also delayed post-fertilization development by altering the head length and locomotor behavior of zebrafish. RNA-sequencing-based DEG analysis showed that SIRT1 and FOXO3a are involved in neurodevelopment. In silico and in vitro analyses showed that aspartame could target and reduce the expression of SIRT1 and FOXO3a proteins in neuron cells. Additionally, aspartame triggered the reduction of autophagy flux by inhibiting the nuclear translocation of SIRT1 in neuronal cells. The findings suggest that aspartame can cause developmental defects and teratogenicity in zebrafish embryos and reduce autophagy by impairing the SIRT1/FOXO3a axis in neuron cells.

Ultrastructure and morphometric characteristics of &lt;i&gt;Oecophylla smaragdina&lt;/i&gt; (Fabricius, 1775) (Hymenoptera: Formicidae)

In this study, we explored various aspects of Oecophylla smaragdina, a potential biocontrol agent, evolution by examining its morphometric characteristics. We employed an intensive All-out search method (AOSM) to gather specimens from multiple locations in Vadakku Karaseri, Tamil Nadu. Our analysis involved measuring 16 morphological traits and indices, including Total Length, Head Width, Head Length, Eye Length and more, using specimens from five colonies in each locality. By calculating various morphometric indices, we assessed specific features and conducted a Principal Component Analysis (PCA) to determine the significance of head-related variables, antennae, and body size in shaping morphometric variation. Our study also revealed positive and negative associations between different morphometric variables, as highlighted by Pearson correlation coefficients. Furthermore, we used a Scanning Electron Microscope to examine the ultrastructure of the abdomen, revealing distinct features such as a one-jointed pedicel and modifications of the poison gland and stings. This comprehensive research provides valuable insights into O. smaragdina morphometric characteristics, enhancing our understanding of its variability and potential adaptations in various habitats.

Collapse of concrete target subjected to embedded explosion of shelled explosive

This paper broadens previous research concerning spalling damage in concrete structures under buried explosions, by additionally examining the effects of shell thickness and shell head length of the warhead experimentally and numerically. In the experiment, concrete targets were subjected to the embedded explosion of cylindrical shelled explosives with different charge masses, shell thicknesses, and shell head lengths. The results reveal that thicker charge shells and longer shell heads decrease the surface area and the depth of spalling damage on the rear surface of concrete structures. In addition, to investigate the damage mechanism and predict the critical collapse thickness (CCT), two- and three-dimensional finite-element models were developed and correlated well with the experimental results. Parametric analyses are also applied to examine how the embedded depth, length-to-diameter ratio, shell thickness, and shell head length affect the CCT for a buried explosion. Finally, an empirical formula is proposed to estimate the CCT based on these factors.

Morphometric evaluation of Aedes aegypti (Linnaeus, 1762) and Culex quiquefasciatus (Say, 1823) (Diptera: Nematocera: Culicidae) of different metamorphosis stages

Morphometric comparison of Aedes. aegypti and Culex. quiquefasciatus larval instars and pupae were done through the measurements of total body length, length of head, thorax and abdomen as well as length and width of different external body parameters. From linear regression of the data from different larval instars showed that the important morphological features were the size of the head, thorax and abdomen of the Ae. Aegypti and Cx. Quinquefasciatus. They increased significantly with the advanced metamorphosis stages (p≤0.05). Size of the external larval organs viz. antennae, comb spine, siphon, anal papilla were also significantly (p≤0.05) increased during stages of metamorphosis. Bangladesh J. Zool. 51(3): 329-343, 2023

Characterization of stmn1a and genetic effects of a 22-bp Indel in its promoter region of bighead carp Hypophthalmichthys nobilis

Stathmin 1 (stmn1) gene, which is involved in the control of cell cycle progression, cell proliferation, differentiation and motility, is a crucial relay in the signal transduction of multiple signaling pathways. Reports on the function of stmn1 in fish are scarce. In this study, the characterization and function of stmn1a gene were explored in an important food fish, namely bighead carp (Hypophthalmichthys nobilis). The bighead carp stmn1a (Hynstmn1a) genomic sequence, which has 2995 bp with an ORF of 447 bp, is evolutionarily conserved in teleost fish. The highest level of expression of Hynstmn1a is in the un-fertilized eggs and spleen of adult bighead carp. The overexpression of Hynstmn1a facilitates cell cycle progression and suppresses apoptosis in EPC cells. In an siRNA assay, disruption of stmn1a in EPC cells resulted in the inhibition of cell cycle progression and promotion of apoptosis. Analysis of promoter activity indicated that an upstream transcription factor (foxo4) regulates Hynstmn1a. Zebrafish mutants with stmn1a knockout by CRISPR/Cas9 exhibited a significant retardation of body length (p ​< ​0.05). There was no significant difference in body weight between stmn1a-mutant zebrafish and wild-type (p ​= ​0.053). A 22-bp Indel in the promoter region of Hynstmn1a with an observed heterozygosity (Ho) of 0.136 in a bighead carp population (n ​= ​191). The polymorphism of this 22-bp Indel genotype is significantly associated with body length (BL), head length (HL) (p ​< ​0.05), body weight (BW), head height (HH), and head width (HW) (p ​< ​0.01), showing its genetic effects on growth promotion. This study sheds light on the function of stmn1a in fish and demonstrates the potential of the 22-bp Indel of Hynstmn1a as a gene marker when selecting breeding individuals for faster growth and a bigger head of bighead carp in aquaculture.

A new loach species of the genus Oreonectes (Teleostei, Cypriniformes, Nemacheilidae) from Guangxi, China.

A new loach species, Oreonectesandongensissp. nov. is described from the Guangxi Zhuang Autonomous Region, China. The new species can be differentiated from other members of the genus by combinations of characters: a developed posterior chamber of the swim bladder, 13-14 branched caudal-fin rays, 8-16 lateral-line pores, body width 12-15% of standard length (SL), interorbital width 42-47% of head length (HL), and caudal peduncle length 11-16% of SL. Bayesian inference phylogenetic analysis based on mitochondrial Cyt b provided strong support for validity of O.andongensissp. nov. (uncorrected p-distance 6.0-7.5%).

A DQN-based memetic algorithm for energy-efficient job shop scheduling problem with integrated limited AGVs

AGVs have gained significant popularity in various industries. However, the existing literature rarely considers the integrated scheduling of production and logistics on the workshop due to the NP-hard property of both machine scheduling and AGV scheduling. The energy-efficient job shop scheduling problem with limited AGVs is investigated in this paper. A multi-objective memetic algorithm with deep Q-network (DQNMMA) is proposed to minimize the makespan and total energy consumption. In DQNMMA, ten features are selected to describe the current state of the population. This enables the DQN to dynamically adjust the crossover probability according to the population evolution. Formulas for calculating the head length and tail length of each node in the disjunctive graph model are presented for the first time to enable fast and accurate access to the critical paths. Building upon the analysis of critical paths, four problem properties are developed as the foundation for designing six neighborhood operators. Then, a property-based variable neighborhood search strategy is proposed to enhance the exploration capability of the algorithm. Numerous experimental results demonstrate that the proposed approaches can effectively enhance the performance of the algorithm, especially in solving large-scale problems. The comparative analysis with three other state-of-the-art multi-objective algorithms confirms the superiority and effectiveness of the proposed DQNMMA.

Examining Fetal Growth Biometrics and Last Menstrual Period Correlation in Minangkabau Ethnicity during Third Trimester Ultrasound

Background Fetal growth significantly impacts well-being and health outcomes at birth, exerting a profound influence on the occurrence of perinatal complications and mortality rates. Aim This study aims to establish normal fetal growth data based on biometric variations in the Minangkabau ethnic group. Methods An analytical cross-sectional study focusing on pregnant women who underwent pregnancy check-ups was conducted in December 2020. Results A total of 520 pregnant women had third trimester ultrasounds. Most were aged 21-39 with one parity, had a senior high school education, and were unemployed. The strongest correlation (R=0.86) was between the last menstrual period (LMP) and biparietal diameter (BPD), while the weakest (R=0.79) was between LMP and head length (HL). All variables were highly significant (p&lt;0.05). Conclusions Fetal growth biometrics (BPD, FL, HC, AC, and HL) were associated with LMP of third trimester ultrasound pregnancy on Minangkabau ethnic.

Patterns of integrated growth of body parts in Rook (Corvus frugilegus) ontogeny.

The early period of ontogeny is key to understanding the patterns of body plan formation in birds. Most studies of avian development have focused on the development of individual avian characters, leaving their developmental integration understudied. We explored the dynamics and integration of relative percentage increments in body mass, lengths of head, skeletal elements of wing and leg, and primary flight feathers in the embryonic and postnatal development of the Rook (Corvus frugilegus). The relative percentage increments were calculated according to Brody's equation. Groups of similar growing traits (modules) were determined using hierarchical cluster analysis, and the degree of correlation between modules was estimated by PLS analysis. The embryonic and postnatal periods demonstrate significant consistency both in the dynamics of changes in relative percentage increments of studied traits as well as in the clustering of individual modules. The modules mainly include the body mass and head length, as well as the elements that form the fore- and hind limbs. Differences were revealed in the combination of modules into clusters in embryonic and postnatal periods. Hind limb elements clustered together with wing elements in the embryonic period but with body mass and the head in the postnatal period. The strongest modularity was noted for the leg in embryogenesis, and for the wing in postnatal development. The forelimb and especially the primary feathers had more distinctive growth patterns. We suggest the changes in the degree of integration between locomotor modules in ontogenesis are connected with the earlier functioning of the legs in the postnatal period and with the preparation of the wings for functioning after a chick leaves the nest.

Estimating Total Length of Partially Submerged Crocodylians from Drone Imagery

Understanding the demographic structure is vital for wildlife research and conservation. For crocodylians, accurately estimating total length and demographic class usually necessitates close observation or capture, often of partially immersed individuals, leading to potential imprecision and risk. Drone technology offers a bias-free, safer alternative for classification. We evaluated the effectiveness of drone photos combined with head length allometric relationships to estimate total length, and propose a standardized method for drone-based crocodylian demographic classification. We evaluated error sources related to drone flight parameters using standardized targets. An allometric framework correlating head to total length for 17 crocodylian species was developed, incorporating confidence intervals to account for imprecision sources (e.g., allometric accuracy, head inclination, observer bias, terrain variability). This method was applied to wild crocodylians through drone photography. Target measurements from drone imagery, across various resolutions and sizes, were consistent with their actual dimensions. Terrain effects were less impactful than Ground-Sample Distance (GSD) errors from photogrammetric software. The allometric framework predicted lengths within ≃11–18% accuracy across species, with natural allometric variation among individuals explaining much of this range. Compared to traditional methods that can be subjective and risky, our drone-based approach is objective, efficient, fast, cheap, non-invasive, and safe. Nonetheless, further refinements are needed to extend survey times and better include smaller size classes.

Comparatively poorer body condition of south-east Indian Ocean pygmy blue whales on their southern migration

The south-east Indian Ocean population of pygmy blue whales (Balaenoptera musculus brevicauda) forages in habitats between temperate foraging grounds off southern Australia and breeding grounds in Indonesian waters. With the opportunity to forage during migration, limited seasonal variation in body condition would be expected. However, increasing numbers of individuals in poor body condition with prominent spinal columns and other features of emaciation have been sighted during their southern migration. This study aimed to measure the morphology and body condition (relative body volume to body length) of pygmy blue whales during their northbound and southbound migration. Unmanned aerial vehicles were used to obtain images of 42 pygmy blue whales (one calf, five juveniles and 36 adults, including one lactating female) in 2021 and 2022. The body lengths ranged from 15.32 to 24.32 m, and the mean relative head length, length to blowhole, width of eyes, fluke width and length of peduncle were 21.8, 18.1, 12.8, 22.9 and 21.3% respectively. There was a significant decrease in body condition of 15.3% between north and southern migrating adult whales. Given the importance of body condition for reproductive success, understanding if this loss is due to natural seasonal variation, or habitat or prey disturbance from environmental environmental or anthropogenic sources, has implications for the future management of the species.

The effect of seed sowing rates on spring durum wheat productivity

The purpose of the current study was to establish the effect of sowing rates of spring durum wheat on its productivity. There has been established that reducing seed sowing rates from 7 to 3 million germinated seeds per 1 ha allows reducing spring durum wheat vegetation period by 6–7 days. There has been identified maximum density of productive stems of the two varieties at a seeding rate of 6 and 7 million germinated seeds per 1 ha. The highest productive tillering capacity for two spring durum wheat varieties was obtained at the variant with a norm of 5 million germinated seeds per 1 ha. Thus, according to the experimental variants, the average plant height of the variety ‘Bezenchukskaya Niva’ was 70.6 cm in the control variant and 81.8 cm at a sowing rate of 5 million germinated seeds per 1 ha. The variety ‘Bezenchukskaya Zolotistaya’ has produced the tallest plants of 79.5 cm, with a seeding rate of 4 million germinated seeds per 1 ha. There has been established that the length of a head also increases with a seeding rate decrease; for example, in the variety ‘Bezenchukskaya Niva’, the maximum indicators of the main head were formed at a seeding rate of 5 million germinated seeds per 1 ha, where the maximum length of the main head was 6.7 cm, the number of grains was 27.5 pieces with a weight of 1.47 g. For the variety ‘Bezenchukskaya Zolotistaya’, the maximum head length was 5.6 cm, and the number of grains was 24 pieces at a rate of 4 million germinated seeds per 1 ha. The fullest grain of the variety ‘Bezenchukskaya Niva’ with 53.4 g of ‘1000-grain weight’ was formed at a seeding rate of 5 million germinated seeds per 1 ha; the variety ‘Bezenchukskaya Zolotistaya’ was 50.4g with a norm of 6 million germinated seeds per 1 ha. The maximum productivity of the variety ‘Bezenchukskaya Niva’ was 3.54 t/ha with a seeding rate of 5 million germinated seeds per 1 ha. The variety ‘Bezenchukskaya Zolotistaya’ formed a yield of 3.23 t/ha with a seeding rate of 6 million germinated seeds per 1 ha.

Analysis of the variability of morphometric and physiological parameters of grain crops when using biofertilizers

Currently, solving the problem of improving agricultural crops’ productivity is of great relevance. The parameters of photosynthetic activity play an important role in photosynthesis and ensure the efficient functioning of plants under various conditions. Understanding of these processes helps better understand the mechanisms of plant growth and development, as well as develop methods to increase productivity and resistance to stress conditions. The purpose of the current study was to estimate the effect of biofertilizers on the functioning of the photosynthetic apparatus and the variability of the area of leaf blades of agricultural grain crops (durum wheat, spring barley), and to establish the dependence of productivity on the ameliorant used. The objects of study were the spring barley variety ‘Anna’ and the durum wheat variety ‘Orenburgskaya’. The area of the leaf blade was measured by scanning using the APFill Ink&amp;Toner Coverage Meter program. To determine the chlorophyll content, there was used a portable N-tester. There has been reliably established positive correlation between productivity increase and the size of the leaf blade of the experimental plants. The application of the studied biofertilizer has had a positive effect on chlorophyll increase in the barley leaf blades. This explains the possibility of changing the studied parameters by agricultural methods (fertilizer application). There has been found a significant correlation (at p˂0.05) between the height parameters with a number of seeds in a head (r = 0.63) and a leaf blade area (r = 0,69), a number of seeds in a head and productivity (r = 0.86). As a result of the study, there has been established a relationship between some quantitative parameters of the seed material (head length – number of seeds in a head), and a positive correlation was identified between a leaf area and a head length (r = 0.69). There has been obtained a significant dependence of barley productivity on the ameliorant used. At the same time, the productivity increase when using fertilizer compared to the control was 58.9 %.

Varietal characteristics of the new barley variety ‘Lyuboyar’ when cultivated with different sowing density

The purpose of the current study was to identify the optimized seeding rate of the spring barley variety ‘Lyuboyar’ to obtain an economically profitable yield in the conditions of the non-blackearth part of the Central region of the Russian Federation on dark gray forest soils of a mean fertility level. The trials were carried out in the conditions of the Ryazan region in the selection crop rotation when sown in “black” fallow in 2022–2023. The trial scheme included the study of 6 options: 3.0; 3.5; 4.0; 4.5; 5.0 and 5.5 million germinating seeds per 1 hectare. There has been established that the optimal option in terms of field germination and preservation of plants for harvesting is the norm of 4.0 million per 1 ha with 89.5 % and 77.5 %, respectively. The number of survived plants before harvesting, the number of productive stems, plant height, head length, number of grains per head and grain weight per head have a significant contribution to crop productivity (r = +0.727...+0.955). The maximum number of stems (924 pcs/m2) and head length (9.2 cm) was demonstrated by the variant with a seeding rate of 4.5 million, height (83 cm) with 5.0 million, productive tillering (3.1) with 5.0–5.5 million, number of grains per head (23.9 pcs.) with 4.0 million, weight of grain per head (1.2 g) with 4.0–4.5 million, 1000-grain weight (47.5 g) with 3.0 million seeds per hectare. It was found that with an increase in the seeding rate, the number of plants increases before harvesting, the number of productive stems, plant height, tillering coefficient and head length increase with r = +0.543...+0.889, but there has been a decrease in indicators such as head weight (r = -0.355) and, especially, 1000-grain weight (r = -0.752). The largest productivity of 7.05 t/ha was obtained with a seeding rate of 4.0 million seeds per hectare, in the second place there was 6.90 t/ha with a rate of 4.5 million seeds per ha. At seeding rates of 4.0–4.5 million germ. seeds per 1 ha, the highest profitability was 67.2–60.2 %.

The morphometric parameters of the biceps brachii: cadaveric study.

The biceps brachii (BB) is a fusiform muscle comprising of two muscular bellies located in the anterior compartment of the arm. Its primary function includes elbow flexion and forearm supination. The study aimed to examine the morphometric parameters of the BB in adult cadaveric specimens. This dissection-based study examined the anatomy of the BB in 40 arms taken from 20 Thiel embalmed European cadavers, including 13 males with an average age of 81 years and seven females with an average age of 84 years. The investigation included an observational inspection of the BB morphology and collected 19 parameters, comprising the lengths and widths of the short and long head tendons and muscle bellies. The observation analysis showed that the anatomy of the BB consisted mainly of two muscle bellies: a short head and a long head. An additional third humeral head, originating from the anteromedial aspect of the mid of the humerus and inserted into the common biceps tendon, was observed in four (10%) specimens. The average lengths of the short head and long head were 35.98 ± 3.44cm and 38.90 ± 3.40cm, respectively. There was no difference in the BB parameters according to the arm sides. However, the male specimens showed greater BB parameters than the female specimens. The short head had a greater muscle belly, while the long head had a longer origin and insertion tendons. The BB parameters were correlated positively with the humerus length.

Long‐term differences in population structure, body size and distribution patterns of amphipods and isopods in wetlands with declining hydroperiods

Abstract In many regions, climatic drying is shortening hydroperiods and freshwater biodiversity is declining. Aquatic species that lack a desiccation‐resistant life stage are predicted to have the least ability to persist in drying climates, yet such species may occur in intermittent waterbodies. We examined the distribution of two crustacean species that lack desiccation‐resistant life stages: the isopod Paramphisopus palustris and amphipod Chiltoniidae sp.nov., before and after the commencement of severe climatic drying in Swan Coastal Plain wetlands, south‐western Australia. Historical distribution data for these species were obtained from studies of the same set of wetlands in 1989–1990. We determined whether population or body size differed between hydrological regimes (perennial, semi‐perennial, seasonal) between 1989–1990 and 2018–2019 for both species. Amphipods, isopods and environmental variables were sampled from 42 wetlands in 2018–2019. Thirty‐three wetlands (22 perennial, 11 seasonal) persisted with the same hydrological regime in both time periods and eight wetlands that were perennial in 1989–1990 had shifted to a drier hydrological regime (four became semi‐perennial, four became seasonal) by 2018–2019. Drying wetland hydrological regimes did not correspond to more limited spatial distributions for either species. Hydrological regime had no effect on amphipod counts, although abundances were lower in 2018–2019 than 1989–1990. In 2018–2019, male amphipods were larger than females in seasonal wetlands, but sexes were the same size in perennial wetlands and females were larger than males in semi‐perennial wetlands. Furthermore, amphipods of both sexes were considerably smaller in semi‐perennial than seasonal or perennial wetlands. Isopod distributions differed between the two sampling periods, with populations primarily lost from wetlands that remained perennial. This unexpected result was likely caused by prolonged periods of high summer–autumn water temperatures and stratification in shallow perennial wetlands that caused anoxia in bottom waters and made surface waters excessively hot for isopods. By contrast, drying seasonal wetlands seemingly offered suitable habitat in summer–autumn. Mean isopod head and body length did not differ between hydrological regimes or sexes, but became smaller between 1989–1990 and 2018–2019 (15 mm average body length in 1989 vs. 8.3 mm in 2018–2019; 17 mm maximum size in 1989–1990 vs. 13.2 mm in 2018–2019). The absence of population losses associated with drying hydrological regimes indicates that the current level of drying is within the tolerance range of both species. However, increased temperatures may be causing body size (and possibly fecundity) to decline for isopods. As global warming continues to shorten wetland hydroperiods in many regions, numerous species will struggle to complete their life cycles, leading to extirpation. Our findings suggest that climate change may also cause conditions in perennial wetlands to exceed the tolerances of species that lack desiccation resistance traits. This emphasises the need to better understand both environmental and habitat changes along the drying trajectory in wetlands and the fundamental life‐history and physiological traits that enable the survival of aquatic invertebrates that lack desiccation resistance. This includes not only species responses to drying, but also responses to other stressors (e.g., prolonged stratification) caused by global warming.