Ecological factors shaping ectoparasite communities on heteromyid rodents at Médanos de Samalayuca.

Rodent ectoparasites are vectors for important pathogens of wildlife, domestic animals, and even zoonosis. Nevertheless, distribution patterns of ectoparasites are not fully understood; habitat, season, and host species are important predictors of distribution and prevalence. Heteromyid rodents are considered important reservoirs of diseases, given the presence of different ectoparasites and pathogens in them, and they offer the opportunity to learn about the ecology of parasites. The aim of the present work was to survey ectoparasites associated with heteromyid rodents near a National Protected Area in Chihuahua Mexico, south of the USA-Mexico border, and asses the effects of ecological factors (season, vegetation type, host species, and host body condition) on parasite infestation. We sampled five different locations from January 2018 to July 2022; 845 heteromyid rodents were examined and 49 fleas and 33 ticks were collected. Ectoparasites belonged to the Siphonaptera and Ixodida orders, including three families Ixodidae (Riphicephalus sanguineus), Pulicidae (Pulex irritans), and Ctenophthalmidae (Meringins altipecten, M. dipodomys). Five species of host rodents were captured, Dipodomys merriami, D. ordii, Chaetodipus eremicus, C. hispidus, and C. intermedius, but the last two species did not present any ectoparasites. Dipodomys merriami presented the highest flea and tick prevalence followed by D. ordii. We found parasitic partnerships between heteromyids according to ecological factors. The infestation in C. eremicus was related to body condition, vegetation type, and sex; in D. merriami, it was related to vegetation type and season, while D. ordii did not present a clear pattern of infestation. Our results suggest that the infestation patterns of heteromyid rodents in desert habitats are species dependent.

Distribution and prevalence of Sin Nombre hantavirus in rodent species in eastern New Mexico.

Orthohantaviruses are diverse zoonotic RNA viruses. Small mammals, such as mice and rats are common chronic, asymptomatic hosts that transmit the virus through their feces and urine. In North America, hantavirus infection primarily causes hantavirus cardiopulmonary syndrome (HCPS), which has a mortality rate of nearly 36%. In the United States of America, New Mexico (NM) is leading the nation in the number of HCPS-reported cases (N = 129). However, no reported cases of HCPS have occurred within eastern NM. In this study, we assessed the prevalence of Sin Nombre virus (SNV) in rodent assemblages across eastern NM, using RT-qPCR. We screened for potential rodent hosts in the region, as well as identified areas that may pose significant infection risk to humans. We captured and collected blood and lung tissues from 738 rodents belonging to 23 species. 167 individuals from 16 different species were positive for SNV RNA by RT-qPCR, including 6 species unreported in the literature: Onychomys leucogaster (Northern grasshopper mouse), Dipodomys merriami (Merriam's kangaroo rat), Dipodomys ordii (Ord's kangaroo rat), Dipodomys spectabilis (Banner-tailed kangaroo rat), Perognathus flavus (Silky pocket mouse), and Chaetodipus hispidus (Hispid pocket mouse). The infection rates did not differ between sexes or rodent families (i.e., Cricetidae vs. Heteromyidae). Generalized linear model showed that disturbed habitat types positively influenced the prevalence of SNV at sites of survey. Overall, the results of this study indicate that many rodent species in east New Mexico have the potential to maintain SNV in the environment, but further research is needed to assess species specific infectivity mechanisms and potential risk to humans.

Dipo: a miniaturized hopping robot via lightweight and compact actuator design for power amplification.

Kangaroo rats are well known as representative hoppers in small-scale animals. Especially kangaroo rats show rapid movement when a predator approaches. If this amazing motion can be applied to small-scale robots, they will be able to traverse lands at high speed while overcoming size limitations. To take advantage of hopping locomotion, in this paper, we present a lightweight and small-scale clutch-based hopping robot called Dipo. To make this possible, a compact power amplifying actuation system has been developed using a power spring and an active clutch. The power spring is possible to take out and use the accumulated energy little by little whenever the robot starts to hop. Moreover, the power spring needs low torque to charge the elastic energy, and a only tiny space is required to install. The active clutch controls the motion of hopping legs by adjusting the timing of energy release and storage. Thanks to these design strategies, the robot weighs 45.07 g, has the height of 5 cm in the stance phase, and achieves the maximum hopping height of 54.9 cm.

The earliest dipodomyine heteromyid in North America and the phylogenetic relationships of geomorph rodents.

Dipodomyine heteromyids (kangaroo rats and mice) are a diverse group of arid-adapted ricochetal rodents of North America. Here, a new genus and species of a large dipodomyine is reported from early Miocene-aged deposits of the John Day Formation in Oregon that represents the earliest record of the subfamily. The taxon is known from a single specimen consisting of a nearly complete skull, dentary, partial pes, and caudal vertebra. The specimen is characterized by a mosaic of ancestral and highly derived cranial features of heteromyids. Specifically, the dental morphology and some cranial characteristics are similar to early heteromyids, but other aspects of morphology, including the exceptionally inflated auditory bullae, are more similar to known dipodomyines. This specimen was included in a phylogenetic analysis comprising 96 characters and the broadest sampling of living and extinct geomorph rodents of any morphological phylogenetic analysis to date. Results support the monophyly of crown-group Heteromyidae exclusive of Geomyidae and place the new taxon within Dipodomyinae. The new heteromyid is the largest known member of the family. Analyses suggest that large body size evolved several times within Heteromyidae. Overall, the morphology of the new heteromyid supports a mosaic evolution of the open-habitat adaptations that characterize kangaroo rats and mice, with the inflation of the auditory bulla appearing early in the group, and bipedality/ricochetal locomotion appearing later. We hypothesize that cooling and drying conditions in the late Oligocene and early Miocene favored adaptations for life in more open habitats, resulting in increased locomotor specialization in this lineage over time from a terrestrial ancestor.

Comparison of genetic variation between rare and common congeners of Dipodomys with estimates of contemporary and historical effective population size.

Species with low effective population sizes are at greater risk of extinction because of reduced genetic diversity. Such species are more vulnerable to chance events that decrease population sizes (e.g. demographic stochasticity). Dipodomys elator, (Texas kangaroo rat) is a kangaroo rat that is classified as threatened in Texas and field surveys from the past 50 years indicate that the distribution of this species has decreased. This suggests geographic range reductions that could have caused population fluctuations, potentially impacting effective population size. Conversely, the more common and widespread D. ordii (Ord's kangaroo rat) is thought to exhibit relative geographic and demographic stability. We assessed the genetic variation of D. elator and D. ordii samples using 3RAD, a modified restriction site associated sequencing approach. We hypothesized that D. elator would show lower levels of nucleotide diversity, observed heterozygosity, and effective population size when compared to D. ordii. We were also interested in identifying population structure within contemporary samples of D. elator and detecting genetic variation between temporal samples to understand demographic dynamics. We analyzed up to 61,000 single nucleotide polymorphisms. We found that genetic variability and effective population size in contemporary D. elator populations is lower than that of D. ordii. There is slight, if any, population structure within contemporary D. elator samples, and we found low genetic differentiation between spatial or temporal historical samples. This indicates little change in nuclear genetic diversity over 30 years. Results suggest that genetic diversity of D. elator has remained stable despite reduced population size and/or abundance, which may indicate a metapopulation-like system, whose fluctuations might counteract species extinction.

Gut Microbial Ecology of Five Species of Sympatric Desert Rodents in Relation to Herbivorous and Insectivorous Feeding Strategies.

The gut microbial communities of mammals provide numerous benefits to their hosts. However, given the recent development of the microbiome field, we still lack a thorough understanding of the variety of ecological and evolutionary factors that structure these communities across species. Metabarcoding is a powerful technique that allows for multiple microbial ecology questions to be investigated simultaneously. Here, we employed DNA metabarcoding techniques, predictive metagenomics, and culture-dependent techniques to inventory the gut microbial communities of several species of rodent collected from the same environment that employ different natural feeding strategies [granivorous pocket mice (Chaetodipus penicillatus); granivorous kangaroo rats (Dipodomys merriami); herbivorous woodrats (Neotoma albigula); omnivorous cactus mice (Peromyscus eremicus); and insectivorous grasshopper mice (Onychomys torridus)]. Of particular interest were shifts in gut microbial communities in rodent species with herbivorous and insectivorous diets, given the high amounts of indigestible fibers and chitinous exoskeleton in these diets, respectively. We found that herbivorous woodrats harbored the greatest microbial diversity. Granivorous pocket mice and kangaroo rats had the highest abundances of the genus Ruminococcus and highest predicted abundances of genes related to the digestion of fiber, representing potential adaptations in these species to the fiber content of seeds and the limitations to digestion given their small body size. Insectivorous grasshopper mice exhibited the greatest inter-individual variation in the membership of their microbiomes, and also exhibited the highest predicted abundances of chitin-degrading genes. Culture-based approaches identified 178 microbial isolates (primarily Bacillus and Enterococcus), with some capable of degrading cellulose and chitin. We observed several instances of strain-level diversity in these metabolic capabilities across isolates, somewhat highlighting the limitations and hidden diversity underlying DNA metabarcoding techniques. However, these methods offer power in allowing the investigation of several questions concurrently, thus enhancing our understanding of gut microbial ecology.

High-Quality Reference Genome for an Arid-Adapted Mammal, the Banner-Tailed Kangaroo Rat (Dipodomys spectabilis).

Kangaroo rats in the genus Dipodomys are found in a variety of habitat types in western North America, including deserts, arid and semiarid grasslands, and scrublands. Many Dipodomys species are experiencing strong population declines due to increasing habitat fragmentation, with two species listed as federally endangered in the United States. The precarious state of many Dipodomys populations, including those occupying extreme environments, make species of this genus valuable subjects for studying the impacts of habitat degradation and fragmentation on population genomic patterns and for characterizing the genomic bases of adaptation to harsh conditions. To facilitate exploration of such questions, we assembled and annotated a reference genome for the banner-tailed kangaroo rat (Dipodomys spectabilis) using PacBio HiFi sequencing reads, providing a more contiguous genomic resource than two previously assembled Dipodomys genomes. Using the HiFi data for D. spectabilis and publicly available sequencing data for two other Dipodomys species (Dipodomys ordii and Dipodomys stephensi), we demonstrate the utility of this new assembly for studies of congeners by conducting inference of historic effective population sizes (Ne) and linking these patterns to the species' current extinction risk statuses. The genome assembly presented here will serve as a valuable resource for population and conservation genomic studies of Dipodomys species, comparative genomic research within mammals and rodents, and investigations into genomic adaptation to extreme environments and changing landscapes.

Elastic energy storage across speeds during steady-state hopping of desert kangaroo rats (Dipodomys deserti).

Small bipedal hoppers, including kangaroo rats, are not thought to benefit from substantial elastic energy storage and return during hopping. However, recent species-specific material properties research suggests that, despite relative thickness, the ankle extensor tendons of these small hoppers are considerably more compliant than had been assumed. With faster locomotor speeds demanding higher forces, a lower tendon stiffness suggests greater tendon deformation and thus a greater potential for elastic energy storage and return with increasing speed. Using the elastic modulus values specific to kangaroo rat tendons, we sought to determine how much elastic energy is stored and returned during hopping across a range of speeds. In vivo techniques were used to record tendon force in the ankle extensors during steady-speed hopping. Our data support the hypothesis that the ankle extensor tendons of kangaroo rats store and return elastic energy in relation to hopping speed, storing more at faster speeds. Despite storing comparatively less elastic energy than larger hoppers, this relationship between speed and energy storage offers novel evidence of a functionally similar energy storage mechanism, operating irrespective of body size or tendon thickness, across the distal muscle-tendon units of both small and large bipedal hoppers.

Comparative analysis of Dipodomys species indicates that kangaroo rat hindlimb anatomy is adapted for rapid evasive leaping.

Body size is a key factor that influences antipredator behavior. For animals that rely on jumping to escape from predators, there is a theoretical trade-off between jump distance and acceleration as body size changes at both the inter- and intraspecific levels. Assuming geometric similarity, acceleration will decrease with increasing body size due to a smaller increase in muscle cross-sectional area than body mass. Smaller animals will likely have a similar jump distance as larger animals due to their shorter limbs and faster accelerations. Therefore, in order to maintain acceleration in a jump across different body sizes, hind limbs must be disproportionately bigger for larger animals. We explored this prediction using four species of kangaroo rats (Dipodomys spp.), a genus of bipedal rodent with similar morphology across a range of body sizes (40-150 g). Kangaroo rat jump performance was measured by simulating snake strikes to free-ranging individuals. Additionally, morphological measurements of hind limb muscles and segment lengths were obtained from thawed frozen specimens. Overall, jump acceleration was constant across body sizes and jump distance increased with increasing size. Additionally, kangaroo rat hind limb muscle mass and cross-sectional area scaled with positive allometry. Ankle extensor tendon cross-sectional area also scaled with positive allometry. Hind limb segment length scaled isometrically, with the exception of the metatarsals, which scaled with negative allometry. Overall, these findings support the hypothesis that kangaroo rat hind limbs are built to maintain jump acceleration rather than jump distance. Selective pressure from single-strike predators, such as snakes and owls, likely drives this relationship.

Immunohistochemistry of kangaroo rat hindlimb muscles.

Kangaroo rats (Dipodomys spp.) use specialized bipedal hopping like that of kangaroos. In contrast to kangaroos that have elastic tendons capable of storing energy, kangaroo rats have inelastic tendons that are unable to store large amounts of energy. Thus, the musculature of the ankle joint provides the greatest power contribution to kangaroo rat hopping. Skeletal muscle can be characterized by several fiber types, including slow twitch (Type I) and fast twitch (Type II) fibers. Fast fibers are found in higher concentration in muscles that perform quick, dynamic movements, whereas slow fibers are found in higher proportion in muscles that perform slow, endurant movements. Using fiber type specific antibodies, we identified four pure (Types I, IIA, IIB, and IIX) and two hybrid (Types I/IIA and IIA/IIX) fiber types in six hindlimb muscles from three kangaroo rats (Dipodomys merriami) to investigate the relationship between fiber composition and hindlimb muscle function. Hindlimb muscles (except soleus) were dominated by Type IIB fibers, which were largest in cross-sectional area, and are known to be best suited for rapid and explosive movements. Oxidative Type IIA and Type IIX fibers were found at moderate concentrations and likely function in maintaining continual saltatory locomotion. Thus, kangaroo rats can use these two fiber type populations as "gears" for both endurant and explosive behaviors.

Plantar flexor muscles of kangaroo rats (Dipodomys deserti) shorten at a velocity to produce optimal power during jumping.

The musculotendon work contributions across all joints during jumping by kangaroo rats are not well understood. Namely, measures of external joint work do not provide information on the contributions from individual muscles or in-series elastic structures. In this study, we examined the functional roles of a major ankle extensor muscle, the lateral gastrocnemius (LG), and a major knee extensor muscle, the vastus lateralis (VL), through in vivo sonomicrometry and electromyography techniques, during vertical jumping by kangaroo rats. Our data showed that both muscles increased shortening and activity with higher jumps. We found that knee angular velocity and VL muscle shortening velocity were coupled in time. In contrast, the ankle angular velocity and LG muscle shortening velocity were decoupled, and rapid joint extension near the end of the jump produced high power outputs at the ankle joint. Further, the decoupling of muscle and joint kinematics allowed the LG muscle to prolong the period of shortening velocity near optimal velocity, which likely enabled the muscle to sustain maximal power generation. These observations were consistent with an LG tendon that is much more compliant than that of the VL.

How to Stick the Landing: Kangaroo Rats Use Their Tails to Reorient during Evasive Jumps Away from Predators.

Tails are widespread in the animal world and play important roles in locomotor tasks, such as propulsion, maneuvering, stability, and manipulation of objects. Kangaroo rats, bipedal hopping rodents, use their tail for balancing during hopping, but the role of their tail during the vertical evasive escape jumps they perform when attacked by predators is yet to be determined. Because we observed kangaroo rats swinging their tails around their bodies while airborne following escape jumps, we hypothesized that kangaroo rats use their tails to not only stabilize their bodies while airborne, but also to perform aerial re-orientations. We collected video data from free-ranging desert kangaroo rats (Dipodomys deserti) performing escape jumps in response to a simulated predator attack and analyzed the rotation of their bodies and tails in the yaw plane (about the vertical-axis). Kangaroo rat escape responses were highly variable. The magnitude of body re-orientation in yaw was independent of jump height, jump distance, and aerial time. Kangaroo rats exhibited a stepwise re-orientation while airborne, in which slower turning periods corresponded with the tail center of mass being aligned close to the vertical rotation axis of the body. To examine the effect of tail motion on body re-orientation during a jump, we compared average rate of change in angular momentum. Rate of change in tail angular momentum was nearly proportional to that of the body, indicating that the tail reorients the body in the yaw plane during aerial escape leaps by kangaroo rats. Although kangaroo rats make dynamic 3D movements during their escape leaps, our data suggest that kangaroo rats use their tails to control orientation in the yaw plane. Additionally, we show that kangaroo rats rarely use their tail length at full potential in yaw, suggesting the importance of tail movement through multiple planes simultaneously.

Estimation of the force-velocity properties of individual muscles from measurement of the combined plantarflexor properties.

The force-velocity (F-V) properties of isolated muscles or muscle fibers have been well studied in humans and other animals. However, determining properties of individual muscles in vivo remains a challenge because muscles usually function within a synergistic group. Modeling has been used to estimate the properties of an individual muscle from the experimental measurement of the muscle group properties. While this approach can be valuable, the models and the associated predictions are difficult to validate. In this study, we measured the in situ F-V properties of the maximally activated kangaroo rat plantarflexor group and used two different assumptions and associated models to estimate the properties of the individual plantarflexors. The first model (Mdl1) assumed that the percent contributions of individual muscles to group force and power were based upon the muscles' cross-sectional area and were constant across the different isotonic loads applied to the muscle group. The second model (Mdl2) assumed that the F-V properties of the fibers within each muscle were identical, but because of differences in muscle architecture, the muscles' contributions to the group properties changed with isotonic load. We compared the two model predictions with independent estimates of the muscles' contributions based upon sonomicrometry measurements of muscle length. We found that predictions from Mdl2 were not significantly different from sonomicrometry-based estimates while those from Mdl1 were significantly different. The results of this study show that incorporating appropriate fiber properties and muscle architecture is necessary to parse the individual muscles' contributions to the group F-V properties.

Individual kinetochore-fibers locally dissipate force to maintain robust mammalian spindle structure.

At cell division, the mammalian kinetochore binds many spindle microtubules that make up the kinetochore-fiber. To segregate chromosomes, the kinetochore-fiber must be dynamic and generate and respond to force. Yet, how it remodels under force remains poorly understood. Kinetochore-fibers cannot be reconstituted in vitro, and exerting controlled forces in vivo remains challenging. Here, we use microneedles to pull on mammalian kinetochore-fibers and probe how sustained force regulates their dynamics and structure. We show that force lengthens kinetochore-fibers by persistently favoring plus-end polymerization, not by increasing polymerization rate. We demonstrate that force suppresses depolymerization at both plus and minus ends, rather than sliding microtubules within the kinetochore-fiber. Finally, we observe that kinetochore-fibers break but do not detach from kinetochores or poles. Together, this work suggests an engineering principle for spindle structural homeostasis: different physical mechanisms of local force dissipation by the k-fiber limit force transmission to preserve robust spindle structure. These findings may inform how other dynamic, force-generating cellular machines achieve mechanical robustness.

Intercontinental test of constraint-breaking adaptations: Testing behavioural plasticity in the face of a predator with novel hunting strategies.

Constraint-breaking adaptations are evolutionary tools that provide a mechanism for incumbent-replacement between species filling similar ecological roles. In common-garden experiments, we exposed populations of two desert rodents to two different viper species, testing their ability to adjust to novel predators that use different hunting strategies. We aimed to understand whether both predators and prey with constraint-breaking adaptations actually manifest comparative advantage over their counterparts. We used convergent species from desert dunes in the Mojave Desert in North America, Merriam's kangaroo rat Dipodomys merriami and the sidewinder rattlesnake Crotalus cerastes, and from the Negev Desert in the Middle East, the greater Egyptian gerbil Gerbillus pyramidum and the Saharan horned viper Cerastes cerastes. Both Mojave species hold constraint-breaking adaptations in relation to their counterparts from the Negev. The rattlesnakes have heat sensing organs (pits) and the kangaroo rats have fur-lined cheek pouches that allow for greater foraging efficiency and food preservation. Using patch-use theory, we evaluated the rodents' risk-assessment from each snake-separately, together and in combination with barn owls. Initially each rodent species foraged less in the presence of its familiar snake, but within a month both foraged less in the presence of the pit-viper (sidewinder). Our findings indicate a level of learning, and behavioural plasticity, in both rodents and ability to assess the risk from novel predators. The kangaroo rats were capable of harvesting far greater amounts of resources under the same conditions of elevated risk. However, the reason for their advantage may lie in bi-pedal agility and not only their ability collect food more efficiently.

Established rodent community delays recovery of dominant competitor following experimental disturbance.

Human activities alter processes that control local biodiversity, causing changes in the abundance and identity of species in ecosystems. However, restoring biodiversity to a previous state is rarely as simple as reintroducing lost species or restoring processes to their pre-disturbance state. Theory suggests that established species can impede shifts in species composition via a variety of mechanisms, including direct interference, pre-empting resources or habitat alteration. These mechanisms can create transitory dynamics that delay convergence to an expected end state. We use an experimental manipulation of a desert rodent community to examine differences in recolonization dynamics of a dominant competitor (kangaroo rats of the genus Dipodomys) when patches were already occupied by an existing rodent community relative to when patches were empty. Recovery of kangaroo rat populations was slow on plots with an established community, taking approximately 2 years, in contrast with rapid recovery on empty plots with no established residents (approx. three months). These results demonstrate that the presence of an established alternate community inhibits recolonization by new species, even those that should be dominant in the community. This has important implications for understanding how biodiversity may change in the future, and what processes may slow or prevent this change.

Exploring Bipedal Hopping through Computational Evolution.

Bipedal hopping is an efficient form of locomotion, yet it remains relatively rare in the natural world. Previous research has suggested that the tail balances the angular momentum of the legs to produce steady state bipedal hopping. In this study, we employ a 3D physics simulation engine to optimize gaits for an animat whose control and morphological characteristics are subject to computational evolution, which emulates properties of natural evolution. Results indicate that the order of gene fixation during the evolutionary process influences whether a bipedal hopping or quadrupedal bounding gait emerges. Furthermore, we found that in the most effective bipedal hoppers the tail balances the angular momentum of the torso, rather than the legs as previously thought. Finally, there appears to be a specific range of tail masses, as a proportion of total body mass, wherein the most effective bipedal hoppers evolve.

Tendons from kangaroo rats are exceptionally strong and tough.

Tendons must be able to withstand the forces generated by muscles and not fail. Accordingly, a previous comparative analysis across species has shown that tendon strength (i.e., failure stress) increases for larger species. In addition, the elastic modulus increases proportionally to the strength, demonstrating that the two properties co-vary. However, some species may need specially adapted tendons to support high performance motor activities, such as sprinting and jumping. Our objective was to determine if the tendons of kangaroo rats (k-rat), small bipedal animals that can jump as high as ten times their hip height, are an exception to the linear relationship between elastic modulus and strength. We measured and compared the material properties of tendons from k-rat ankle extensor muscles to those of similarly sized white rats. The elastic moduli of k-rat and rat tendons were not different, but k-rat tendon failure stresses were much larger than the rat values (nearly 2 times larger), as were toughness (over 2.5 times larger) and ultimate strain (over 1.5 times longer). These results support the hypothesis that the tendons from k-rats are specially adapted for high motor performance, and k-rat tendon could be a novel model for improving tissue engineered tendon replacements.

The Contributions of Individual Muscle-Tendon Units to the Plantarflexor Group Force-Length Properties.

The combined force-length (F-L) properties of a muscle group acting synergistically at a joint are determined by several aspects of the F-L properties of the individual musculotendon units. Namely, misalignment of the optimal lengths of the individual muscles will affect the group F-L properties. This misalignment, which we named [Formula: see text], arises from the properties of the muscles (i.e., optimum fiber length and pennation angle) and of their tendons (i.e., compliance and slack length). The aim of this study was to measure the F-L properties of kangaroo rat plantarflexors as a group and individually and determine the effects of [Formula: see text] on the group F-L properties. Specifically, we performed a sensitivity analysis to quantify how [Formula: see text] influences the tradeoff between maximizing the peak force vs. having a wider group F-L curve. In the kangaroo rat, we found that the optimal lengths of two bi-articular musculotendon units, the plantaris and the gastrocnemius, were misaligned by 1.8 mm, but this amount favored maximal peak force rather than increasing F-L curve width. Because we measured the misalignment in situ, we could directly assess the tradeoff between maximizing peak force vs. a wider F-L curve without making modeling assumptions about the individual muscle or tendon properties.