Positive Allometric Relationship Research Articles

Life history of sprat (Sprattus sprattus) in the Black Sea under warming and fishing: current state and patterns of variability.

Sprat Sprattus sprattus (Linnaeus, 1758) is one of the most significant commercial fish species in the Black Sea. This study examines the sex ratio, size-age structure, growth, and mortality of sprat in the waters of Crimea from 2021 to 2023. The paper discusses the geographic variability and the influence of temperature, food availability, and fishing pressure on the life history of this species. In total, 2113 individuals from commercial catches were examined. The sex ratio was slightly skewed towards females (1:0.83). The maximum total length for both males and females was 10.0 cm, with a maximum weight of 8.51 g for females and 6.73 g for males. The lifespan for both sexes was 4 years. The Bertalanffy growth equation parameters were calculated, with L∞ = 13.79 cm, W∞ = 16.3 g, K = 0.237 year-1 and t0 = -1.53 year. The exponent value in the length-weight relationship was 3.14 (positive allometric relationship). The total, natural and fishing mortality coefficients for both sexes were 2.13, 0.65 and 1.48 year-1, respectively, and the exploitation ratio was 0.70, indicating excessive fishing pressure. It was determined that sprat from lower latitudes had smaller sizes, slower growth rates and shorter lifespans compared to sprat from higher latitudes. A strong negative correlation was found between the size and lifespan of sprat and sea surface temperature. Excessive fishing pressure against the backdrop of climate warming was identified as the cause of the reduction in lifespan and size of sprat in the Black Sea, therefore it is recommended to reduce the volume of sprat fishing and increase its minimum landing size to preserve the population of sprat in the Black Sea.

Condtion Factor and Gonadosomatic Index Study of Nilem (Osteochilus hasselti) Catch in Teluk Lake, Jambi

The nilem fish (Osteochilus hasselti) is one of the most easily caught fish in Teluk Lake. Currently, cage farming activity in the lake slightly exceeds the water carrying capacity, which is suspected to affect the life of fish in the lake, including nilem. This study aimed to determine the condition factor and Gonadosomatic Index (GSI) of the nilem catch in the lake. This study was conducted from August to September 2023 in Teluk Lake. This research used a survey method with simple census sampling techniques. The analysis of the length-weight relationship of nilem fish obtained from Teluk Lake showed a positive allometric relationship with a value of b = 3.7148. It showed that the increase in body weight of nilem fish was not linear with the increase in length. The catch results by fishermen for nilem fish found a male-to-female sex ratio of 1:2.15, with 90% of the captured fish in a mature gonad condition. The GSI for females ranged from 3.20% to 8.33% and for males, from 0.03% to 28.89%. The first maturation size (Lm) for male fish was 125.847, with a size class range of 116–126 mm. For female fish, the first maturation size calculation resulted in 112.996 with a size range in the 104–113 mm class. Lm is smaller than the average size of the captured fish, indicating that it is safe to catch, and there is a low likelihood of recruitment overfishing. Keywords: GSI, Lm, Osteochilus hasselti, positive allometric, Teluk Lake.Top of FormBottom of Form

Water deficit affects the nitrogen nutrition index of winter wheat under controlled water conditions

Water deficit affects the nitrogen nutrition index of winter wheat under controlled water conditions

Space use of invertebrates in terrestrial habitats: Phylogenetic, functional and environmental drivers of interspecific variations

Abstract AimWe present the first global database of movement patterns of terrestrial invertebrates, focusing on active dispersal and foraging movements. We depict interspecific variations in movement distances among invertebrates and assess potential drivers of these variations. We finally contrast our results with those of previous vertebrate studies.LocationWorldwide.MethodsWe conducted a meta‐analysis using 176 studies. They provided 411 movement estimates: 175 foraging movement estimates for 101 species, 51 families and 19 orders, and 236 dispersal estimates for 131 species, 53 families and 16 orders. These estimates were complemented by several organism functional traits: body mass, diet, locomotion mode and by environmental variables of the study sites: temperature and NDVI. We computed allometric relationships between movement distances and body mass both globally and separately for each taxonomic order with sufficient data. We tested the relative influence of the co‐variables on movement distances through model selection.ResultsWe reveal a general positive allometric relationship between movement distance and body mass that holds across most taxonomic orders. We evidence a strong phylogenetic signal in movement distances that translates in variable allometries of movement distances with body mass across taxonomic orders. We further find that interspecific variations of movement distances are primarily correlated with functional differences rather than environmental conditions. Locomotion mode is the most important explanatory variable of both dispersal and foraging distances, with larger distances among flying individuals followed by walking and crawling ones for a given body mass. Surprisingly, trophic guild has a low predictive power of invertebrate movement distances as opposed to vertebrates, with unclear differences between invertebrate carnivores, herbivores and decomposers.Main ConclusionsOur study provides general allometric equations for terrestrial movement distances of invertebrates. It further reveals important functional drivers of their interspecific variation in space use with a dominant role of their evolutionary history.

Growth allometry and dental topography in Upper Triassic conodonts support trophic differentiation and molar-like element function

Abstract Conodont elements have high rates of morphological evolution, but the drivers of this disparity are debated. Positive allometric relationships between dimensions of food-processing surfaces and entire P1 elements have been used to argue that these elements performed mechanical digestion. If involved in food processing, the surface of the element should grow at a rate proportional to the increase in energy requirements of the animal. This inference of function relies on the assumption that the energy requirements of the animal grew faster (≅ mass0.75) than the tooth area (≅ mass0.67). We reevaluate this assumption based on metabolic rates across animals and calculate the allometry in platform-bearing P1 elements of Late Triassic co-occurring taxa, Metapolygnathus communisti and Epigondolella rigoi, using 3D models of ontogenetic series. Positive allometry is found in platform and element dimensions in both species, supporting a grasping-tooth hypothesis, based on the assumption that metabolic rate in conodonts scaled with body mass similarly to that in fish and ectotherms. We also calculate the curvature of the P1 platform surface using the Dirichlet normal energy (DNE) as a proxy for diet. DNE values increase with body mass, supporting the assumption that conodont metabolic rates increased faster than mass0.67. We finally find that adults in both taxa differ in their food bases, which supports trophic diversification as an important driver of the remarkable disparity of conodont elements.

Contamination effects on sexual selection in wild dung beetles.

Sexual selection influences the expression of secondary sexual traits, which are costly to produce and maintain and are thus considered honest indicators of individual condition. Therefore, sexual selection could select for high-quality individuals able to respond to stressful conditions, with impacts on population-level fitness. We sampled dung beetles from 19 pastures and investigated if contamination by herbicides and veterinary drugs modifies male investment in sexually selected traits and has associated population-level effects. We measured horn size, condition dependence (i.e. size-corrected body mass) and allometry, besides abundance and sexual size dimorphism in three species: Copris incertus, Euoniticellus intermedius and Digitonthophagus gazella. In contrary to our expectations, horn size was independent of contamination and individual condition. However, strong positive allometric relationships were reduced by herbicide contamination for C. incertus and D. gazella and were increased by ivermectin for C. incertus, revealing differential investment in horn production according to body size in contaminated habitats. At the population level, large-horned C. incertus males were more abundant in contaminated pastures, potentially revealing a case of evolutionary rescue by sexual selection or a plastic response to higher population densities. Finally, chemical compounds affected the sexual size dimorphism of all three species, with potential effects on female fecundity or intrasexual selection. Together, our findings indicate that contamination interferes with sexual selection processes in the wild, opening new questions regarding the role of sexual selection in favouring species persistence in contaminated environments.

Age and growth of Antarctic deep-sea smelt (Bathylagus antarcticus), an important mesopelagic fish in the Southern Ocean

Age and growth of Antarctic deep-sea smelt (Bathylagus antarcticus), an important mesopelagic fish in the Southern Ocean

Age and growth of early-life-stage Atlantic tarpon (Megalops atlanticus) from the northcentral Gulf of Mexico.

Age and growth of early-life-stage Atlantic tarpon Megalops atlanticus collected from Mississippi coastal waters in the northcentral Gulf of Mexico (GOM) are described using otolith microstructure analysis. Tarpon leptocephali (n= 95, 16.0-27.8 mm standard length, LS ) collected from June throughOctober 2013-2018, ranged in age from 22 to 43 days (mean=30.9± 0.5 days). Leptocephalus somatic growth rates ranged 0.46-1.24 mm day-1 (mean=0.76 ± 0.02 mm day-1 ), and leptocephalus otolith growth rates ranged 1.78-3.97 μm day-1 (mean=2.58 ± 0.04 μm day-1 ). Growth rates were inversely correlated to leptocephalus age, indicating the shrinkage phase associated with leptocephalus metamorphosis. Juvenile tarpon (n= 358, 50-359 mm fork length, LF ) were collected from August through December 2007-2018. Juveniles exhibited a positive allometric relationship (adjusted R2 = 0.99, P< 0.001) between length and mass. The age of 100 juveniles (71-277 mm LF ) ranged from 76 to 174 days. Juvenile growth rate was estimated as 1.56 ± 0.11 mm day-1 . Significant (P< 0.001) linear relationships were found between juvenile age and otolith metrics, including otolith mass (R2 = 0.81) and radius (R2 = 0.68). Evaluation of the backcalculated hatch dates suggests that specimens in the collection hatched from late May through mid-September with slight peaks during July and August. A Rao's Spacing Test of Uniformity indicates the presence of significant lunar periodicity in leptocephalus hatch dates (n= 95, U= 250.1, P< 0.05), with 50% of the leptocephali hatched within 5 days (before or after) of the full moon. This study fills critical gaps in the scientific knowledge of tarpon and provides estimates of early-life-history metrics for an iconic game fish at the northernmost extent of its GOM range.

Exposure to Atrazine Impairs Behaviour and Growth Performance in African Catfish, Clarias gariepinus (Burchell, 1822) Juveniles

Clarias gariepinus juveniles of average weight, 17.57±1.95 g and an average length of 14.26±0.39 cm were exposed to environmentally relevant concentrations of 0 (control), 2.5, 25, 250, and 500 µg L-1 atrazine in a quality-controlled 28-day bioassay. Growth performance was assessed bi-weekly and fish samples were taken from different tanks to determine the relative growth rate, specific growth rate, feed conversion ratio, condition factor and behaviour. At the end of two weeks of exposure, the relative growth rate and the specific growth rate among exposed fish groups was found to reduce significantly (p&lt;0.05) compared to the control, an indication of poor growth performance. The average specific growth rates (SGR) of control fish is 3.86±0.02 %/w at the end of the exposure duration while recording -0.64±0.09 in the 500 µg L-1 group. Feed conversion ratio increased significantly from control to the group with highest atrazine concentration. Condition factor (K) of fish among treatment groups showed significant decrease in values with increasing concentration of atrazine in a dose-dependent pattern. Atrazine exposure resulted in behavioural anomalies including erratic swimming, clinging to the water surface, loss of equilibrium, lethargy, and discolouration. The behavioural responses were found to be concentration-dependent. The length-weight relationships for both control and atrazine exposed fish exhibited positive allometric growth and significant relationships as depicted by the value of R2 (coefficient of determination) except in the fish group exposed to 500 µg L-1 atrazine which exhibited negative allometric growth. Findings from this study indicate interference with normal behaviour and growth performance of C. gariepinus juveniles with ecological implications in water bodies exposed to atrazine even at reduced concentrations.

Tracking movements of decapod crustaceans: a review of a half-century of telemetry-based studies

Decapod crustaceans are ecologically and economically important invertebrates but are vulnerable to anthropogenic pressures and climate change. Understanding their spatial ecology is essential for their management and conservation, with telemetry emerging as a useful tool to quantify space-use and movements. Here, we synthesized the use of telemetry to study decapods among articles published from 1971 to 2019 (n = 102 studies), by taxonomic group of the study species, study location, objectives, number of animals tagged and their tag recovery rate, types (and trends) of telemetry used, and IUCN conservation status. These studies revealed insight into the behaviours and roles of decapods across habitats and geographic regions. The most common study species were crayfish and lobsters (41%, Astacidea), and these studies also had the highest number of individuals tagged per study (mean = 149 individuals). Most studies (86%) were conducted in the northern hemisphere. Acoustic tags were the most commonly used equipment (66% of studies) and were first employed in 1971, followed by radio-telemetry (mid-1990s), passive integrated transponders (mid-2000s), and data storage tags (late 2000s). Almost half (48%) of studies focused on species that had a conservation status of Least Concern, perhaps reflecting an applied science focus on animals of commercial interest rather than conservation importance. The positive allometric relationship between body length and movement rate (exponent = 0.86) demonstrates the type of broader ecological insight that combining these studies can provide. Tracking decapod movements will likely become increasingly important for managing fisheries, protecting sensitive species, and understanding invasion biology.

Scaling of petiole anatomies, mechanics and vasculatures with leaf size in the widespread Neotropical pioneer tree species Cecropia obtusa Trécul (Urticaceae).

Although the leaf economic spectrum has deepened our understanding of leaf trait variability, little is known about how leaf traits scale with leaf area. This uncertainty has resulted in the assumption that leaf traits should vary by keeping the same pace of variation with increases in leaf area across the leaf size range. We evaluated the scaling of morphological, tissue-surface and vascular traits with overall leaf area, and the functional significance of such scaling. We examined 1,271 leaves for morphological traits, and 124 leaves for anatomical and hydraulic traits, from 38 trees of Cecropia obtusa Trécul (Urticaceae) in French Guiana. Cecropia is a Neotropical genus of pioneer trees that can exhibit large laminas (0.4m2 for C. obtusa), with leaf size ranging by two orders of magnitude. We measured (i) tissue fractions within petioles and their second moment of area, (ii) theoretical xylem hydraulic efficiency of petioles and (iii) the extent of leaf vessel widening within the hydraulic path. We found that different scaling of morphological trait variability allows for optimisation of lamina display among larger leaves, especially the positive allometric relationship between lamina area and petiole cross-sectional area. Increasing the fraction of pith is a key factor that increases the geometrical effect of supportive tissues on mechanical rigidity and thereby increases carbon-use efficiency. We found that increasing xylem hydraulic efficiency with vessel size results in lower leaf lamina area: xylem ratios, which also results in potential carbon savings for large leaves. We found that the vessel widening is consistent with hydraulic optimisation models. Leaf size variability modifies scaling of leaf traits in this large-leaved species.

Evaluation of some Essential and Toxic Metals in farmed Ctenopharyngodonidella in relation to Body Size and Condition Factor

Basic aim of this research was to determine levels of some metals (Ca, Cd, Cr, Co, Cu, Fe, K, Mn, Ni, Na, Pb Zn) and their relationships to body size and condition factor in the whole body of Ctenopharyngodon idella (Grass carp). Concentrations of these elements were assessed in 55 fish samples of different size, randomly collected in January, 2015, from a private fish farm by ICP-OES after wet digestion method. Results of the study showed that analyzed elements were found within normal ranges. Ca, Cu, Fe, K, Mn, Na and Zn had highly significant relationships with fish size. Cd, Pb, Cu, K, Mn, Ni, Na, increased isometrically while Cr, Co, Zn, had negative allometric relationship and Fe and Ca showed positive allometric relationship with rise in weight of C. idella. Moreover, Ni, Mn, Pb and Cd represented isometric increase whereas Na, K, Zn, Fe and Ca had positive allometry; and Co, Cu, Cr had negative allometry with increase in total length of the fish. Most of inter-elemental relationships showed. Multiple regressions analyses showed positive correlation for Fe, Cu, Zn, Mn, Pb, Na, K, Ca and Ni had highly significant relations with total length and body weight.

Age and growth of Brauer's lanternfish Gymnoscopelus braueri and rhombic lanternfish Krefftichthys anderssoni (Family Myctophidae) in the Scotia Sea, Southern Ocean.

This study examines age and growth of Brauer's lanternfish Gymnoscopelus braueri and rhombic lanternfish Krefftichthys anderssoni from the Scotia Sea in the Southern Ocean, through the analysis of annual growth increments deposited on sagittal otoliths. Otolith pairs from 177 G. braueri and 118 K. anderssoni were collected in different seasons from the region between 2004 and 2009. Otolith-edge analysis suggested a seasonal change in opaque and hyaline depositions, indicative of an annual growth pattern, although variation within the populations of both species was apparent. Age estimates varied from 1 to 6 years for G. braueri (40 to 139 mm standard length; LS ) and from 0 to 2 years for K. anderssoni (26 to 70 mm LS ). Length-at-age data were broadly consistent with population cohort parameters identified in concurrent length-frequency data from the region for both species. The estimated values of von Bertalanffy growth curves for G. braueri were L∞ = 133.22 mm, k = 0.29 year-1 and t0 = -0.21 year and the values for K. anderssoni were L∞ = 68.60 mm, k = 0.71 year-1 and t0 = -0.49 year. There were no significant (P > 0.05) differences in growth between sexes for either species, suggesting that males and females have similar growth and development trajectories in the Scotia Sea. A positive allometric relationship between LS and wet mass was found for each species, as well as a significant (P < 0.0001) linear relationship between otolith size and LS . Growth performance (Ф') was similar between the two species and congruent with other myctophid species across the Southern Ocean. This study provides important parameters for future Southern Ocean ecosystem studies in a resource management context.

What determines the number of auditory sensilla in the tympanal hearing organs of Tettigoniidae? Perspectives from comparative neuroanatomy and evolutionary forces

Insects have evolved complex receptor organs for the major sensory modalities. For the sense of hearing, the tympanal organ of Tettigoniidae (bush crickets or katydids) shows remarkable convergence to vertebrate hearing by impedance conversion and tonotopic frequency analysis. The main auditory receptors are scolopidial sensilla in thecrista acustica. Morphological studies established that the numbers of auditory sensilla are species-specific. However, the factors determining the specific number of auditory sensilla are not well understood. This review provides an overview of the functional organization of the auditory organ in Tettigoniidae, including the diversification of thecrista acusticasensilla, a list of species with the numbers of auditory sensilla, and a discussion of evolutionary forces affecting the number of sensilla in thecrista acusticaand their sensitivity. While all species of Tettigoniidae studied so far have acrista acustica, the number of sensilla varies on average from 15–116. While the relative differences or divergence in sensillum numbers may be explained by adaptive or regressive changes, it is more difficult to explain a specific number of sensilla in thecrista acusticaof a specific species (like for the model speciesAncistrura nigrovittata,Copiphora gorgonensis,Gampsocleis gratiosa,Mecopoda elongata,Requena verticalis, orTettigonia viridissima): sexual and natural selection as well as allometric relationships have been identified as key factors influencing the number of sensilla. Sexual selection affects the number of auditory sensilla in thecrista acusticaby the communication system and call patterns. Further, positive allometric relationships indicate positive selection for certain traits. Loss of selection leads to evolutionary regression of the auditory system and reduced number of auditory sensilla. This diversity in the auditory sensilla can be best addressed by comparative studies reconstructing adaptive or regressive changes in thecrista acustica.

Relative growth, sexual maturity and handedness in the ghost shrimp &lt;em&gt;Callichirus major&lt;/em&gt; (Decapoda: Callianassidae) from the southwestern Atlantic

Biometric studies provide valuable information about changes associated with the growth and sexual maturity of living organisms. We analysed sexual dimorphism, allometric growth, sexual maturity and handedness in the ghost shrimp Callichirus major at Gonzaga beach, Brazil, where the catches of this species have been prohibited since 1992. To this end, a total of 544 individuals of C. major were collected during 12 months of sampling. Males were significantly smaller than females, denoting sexual dimorphism with respect to body size. The analysis of allometric growth between chelar carpus length and carapace length (CL) revealed a positive allometric relationship in juveniles of both sexes and adult males, but a negative allometry in adult females. Overall, our results showed the existence of two main growth phases related to sexual maturity, with a similar transition point for males (15.0 mm CL) and females (16.0 mm CL). Heterochely and homochely were registered in shrimp from both sexes, but in males heterochely occurred to a higher degree and was predominant (86.9%), whereas in females homochely was slightly more frequent (59.3%). The consequences of sexual dimorphism in terms of body size and chelipeds in the mating system of C. major are discussed in this study.

Mechanical similarity across ontogeny of digging muscles in an Australian marsupial (Isoodon fusciventer).

Many mammals dig, either during foraging to access subsurface food resources, or in creating burrows for shelter. Digging requires large forces produced by muscles and transmitted to the soil via the skeletal system; thus fossorial mammals tend to have characteristic modifications of the musculoskeletal system that reflect their digging ability. Bandicoots (Marsupialia: Peramelidae) scratch-dig mainly to source food, searching for subterranean food items including invertebrates, seeds, and fungi. They have musculoskeletal features for digging, including shortened, robust forelimb bones, large muscles, and enlarged muscle attachment areas. Here, we compared changes in the ontogenetic development of muscles associated with digging in the Quenda (Isoodon fusciventer). We measured muscle mass (m m ), pennation angle, and fiber length (FL) to calculate physiological cross-sectional area (PCSA; a proxy of maximum isometric force) as well as estimate the maximum isometric force (Fmax) for 34 individuals ranging in body size from 124 to 2,390 g. Males grow larger than females in this bandicoot species, however, we found negligible sex differences in mass-specific m m , PCSA or FL for our sample. Majority of the forelimb muscles PCSA showed a positive allometric relationship with total body mass, while m m and FL in the majority of forelimb muscles showed isometry. Mechanical similarity was tested, and two thirds of forelimb muscles maximum isometric forces (Fmax) scaled with isometry; therefore the forelimb is primarily mechanical similar throughout ontogeny. PCSA showed a significant difference between scaling slopes between main movers in the power stroke, and main movers of the recovery stroke of scratch-digging. This suggests that some forelimb muscles grow with positive allometry, specially these associated with the power stroke of digging. Intraspecific variation in PCSA is rarely considered in the literature, and thus this is an important study quantifying changes in muscle architectural properties with growth in a mammalian model of scratch-digging.

Aboveground and Belowground Biomass Relationships in the Zoige Peatland, Eastern Qinghai–Tibetan Plateau

Plant biomass and its allocation patterns are instrumental in understanding global carbon sinks; however, knowledge is still limited, especially in high-altitude peatlands. We investigated aboveground and belowground biomass allocation in the Zoige peatland of the Tibetan plateau, China, and its relationship with environmental factors using data collected from 32 sites across the peatland during 2011 and 2012. Standardized major axis, multiple factor analysis and linear regression functions were used to perform data analysis. The average aboveground biomass, belowground biomass, total biomass and root:shoot ratio for the Zoige alpine peatland were 341.01, 3262.93, 3620.36 g m−2 and 10.32, respectively. On average, approximately 86% of the root biomass was located in the top 30 cm of soil. There was positive allometric relationship (p < 0.01) between belowground biomass and aboveground biomass. The water conditions, soil organic carbon and soil nitrogen were the main factors that influenced plant biomass and biomass allocation in the Zoige peatland.

Reproducción de los róbalos Centropomus undecimalis y C. ensiferus (Perciformes: Centropomidae) en una laguna costera tropical

Snooks C. undecimalis and C. ensiferus are important fishery resources in their distribution area. In Venezuela they are caught by artisanal fisheries along the entire coast. However, studies on their biology that would help establish fishing regulations are scarce. To study reproduction aspects of these species, we analyzed 1 325 individuals of C. undecimalis and 2 025 of C. ensiferus caught by artisanal fishing in the Laguna de Tacarigua in Northern Venezuela, from July 2009 to September 2010. Total length, total weight, sex and stage of gonadal development were recorded. The sex ratio varied throughout the year: there was a significant difference in favor of C. undecimalis males (1.5:1), and C. ensiferus females (1:3.3). Differences were also evident in the sexual proportion at each size group. For both species, males dominated in the lower size ranges while females dominated in the larger size ranges. These results suggested sequential hermaphroditism (protrandry) in both species. Size at sexual maturity (Lm50) for C. undecimalis was ♀= 73.6 and ♂= 59.3 cm, and ♀= 26 and ♂= 21.5 cm for C. ensiferus. C. ensiferus reproduced throughout the year with two periods of higher intensity (August to September and February to April). Although we found very few mature individuals for C. undecimalis, February showed an important reproduction peak. Growth differences were found between males and females of C. undecimalis: positive allometry for females (P= 0.0022*L3.353) and negative allometry for males (P= 0.0108*L2.945). Both males and females of C. ensiferus showed a positive allometric relationship (P= 0.0049*L3.235). Lack of fishing regulations and controls, evidenced in this study by significant volumes of immature individuals in the catches, and the particular reproductive biology of these species, strongly indicates the need to establish regulations to ensure their responsible use. We recommend establishing a closed season during the first quarter of the year and minimum catch sizes for both species.

Morphometrics, sex ratio, sexual size dimorphism, biomass, and population size of the Nile crocodile (Crocodylus niloticus) at its southern range limit in KwaZulu-Natal, South Africa

Animal body size and sex are requisite data for understanding population structure and demography. Little information exists regarding Nile crocodile, Crocodylus niloticus, morphometrics, sex ratios of wild populations, sexual size dimorphism and standing crop biomass. We captured 322 C. niloticus at Lake St Lucia and Ndumo Game Reserve, South Africa, the two largest crocodile populations at the southern extent of the species’ range in Africa, and measured a suite of physical characteristics to create predictive models of body length from other morphological attributes and body mass. Our sample included 118 hatchlings, 91 subadults and 113 adults. Strong positive allometric relationships were found between body length metrics (total length and snout-vent length) and other morphometrics. All morphometric regressions were linear, with the exception of the relationship of body length to body mass, which was logarithmic. Among relationships of cranial morphology and body length, we found considerable individual variation among all size classes. The mean head width-to-head length ratio was 1.9 ± 1.6, and mean head length-to-total length ratio was 0.14 ± 0.005. The sex ratios for non-hatchling individuals at both populations were essentially 1:1, but adult sex ratios were male biased. We calculated a total standing crop biomass of 96,867.18 kg (161.45 kg/km) and 52,640.40 kg (1504.01 kg/km) for C. niloticus at Lake St Lucia and Ndumo Game Reserve, respectively, and an estimated 3650 non-hatchling individuals for the province of KwaZulu-Natal. The data presented here will help inform crocodile management and population surveys in South Africa, where C. niloticus is an important apex predator that partitions aquatic resources and occasionally comes into conflict with human beings.

Sexual dichromatism in wing pigmentation of New World dragonflies follows Rensch's rule.

Many animal taxa that display sexual size dimorphism (SSD) exhibit a positive allometric relationship in which the degree of dimorphism increases with body size. This macroevolutionary pattern is known as Rensch's rule. Although sexual selection is hypothesized to be the main mechanism causing this pattern, body size is influenced by several selective forces, including natural and sexual selection. Therefore, by focusing exclusively on SSD one cannot ascertain which of these selective forces drives Rensch's rule. If sexual selection is indeed the main mechanism underlying Rensch's rule, we predict that other sexually selected traits, including coloration-based ornaments, will also exhibit interspecific allometric scaling consistent with Rensch's rule. We tested this prediction using wing pigmentation of 89 species of dragonflies. Studies show that male wing pigmentation is generally under strong intra- and intersexual selection, so that sexual dichromatism in this trait should follow Rensch's rule. Conversely, the available evidence suggests that male body size is usually not sexually selected in dragonflies, so we do not expect SSD to follow Rensch's rule. First, we found that sexual dichromatism in wing pigmentation was consistent with Rensch's rule. The phylogenetic major axis regression slope was significantly greater than one. We also showed that the allometric slope for SSD was not different from unity, providing no support for Rensch's rule. Our results provide the first evidence that a trait which appears to be under strong sexual selection exhibits a pattern consistent with Rensch's rule.