Tail Breaks Research Articles

Tail bifurcation in Chinese blue-tailed skink Plestiodon chinensis (Gray, 1839)

Caudal autotomy is a strategy widely used in lizards to avoid predation. In some cases, tail breaks but it does not detach completely from the body, leading to a regenerated tail with multiple tips. In this note, we reported two tail bifurcation individuals of Plestiodon chinensis found on a farm. The X-rays showed that the branches of these two individuals are not ossified, but form cartilage behind the fracture surface of the tail. The present findings will provide information for studying tail regeneration abnormalities in lizards.

Coordinated alternation of DNA methylation and alternative splicing of PBRM1 affect bovine sperm structure and motility

ABSTRACT DNA methylation and gene alternative splicing drive spermatogenesis. In screening DNA methylation markers and transcripts related to sperm motility, semen from three pairs of full-sibling Holstein bulls with high and low motility was subjected to reduced representation bisulphite sequencing. A total of 948 DMRs were found in 874 genes (gDMRs). Approximately 89% of gDMR-related genes harboured alternative splicing events, including SMAD2, KIF17, and PBRM1. One DMR in exon 29 of PBRM1 with the highest 5mC ratio was found, and hypermethylation in this region was related to bull sperm motility. Furthermore, alternative splicing events at exon 29 of PBRM1 were found in bull testis, including PBRM1-complete, PBRM1-SV1 (exon 28 deletion), and PBRM1-SV2 (exons 28–29 deletion). PBRM1-SV2 exhibited significantly higher expression in adult bull testes than in newborn bull testes. In addition, PBRM1 was localized to the redundant nuclear membrane of bull sperm, which might be related to sperm motility caused by sperm tail breakage. Therefore, the hypermethylation of exon 29 may be associated with the production of PBRM1-SV2 in spermatogenesis. These findings indicated that DNA methylation alteration at specific loci could regulate gene splicing and expression and synergistically alter sperm structure and motility.

Recognition of Coat Pattern Variation and Broken Tail Phenomenon in the Asiatic Golden Cat (Catopuma temminckii).

Simple SummaryA variety of new survey technologies are continuously being developed and used in wildlife monitoring. Rapidly advancing and widely used camera trap survey technology has helped to capture data and gain insights into many species. The Eastern Himalayas is a global biodiversity hotspot with exceptionally high species diversity. The Asian golden cat is widely distributed in the Yarlung Zangbo Grand Canyon National Nature Reserve. It inhabits seasonal rain forests from 100 m above sea level to the Rhododendron forest up to 3500 m above sea level. Coat pattern variation in the Asian golden cat is particularly prominent in this region. The common color type is the most widely distributed, followed by nine other types. We found 10 coat pattern variations and two coat patterns with a broken tail made up 0.32% of independent photos taken during a long-term nine-year monitoring program. The variation in coat patterns is indicative of the geography of the region. Environmental conditions regulate and activate the genetic diversity of Asian golden cat phenotypes. This study further strengthened the understanding of the basic knowledge of golden cat color types and lays the foundation for exploring the diversity of golden cat color types at the molecular level.The Asian golden cat (Catopuma temminckii) is the most varied wild cat species in terms of coat color. Understanding coat pattern variation will help to elucidate the mechanisms behind it as well as its relationship with the environment. We conducted long-term (2013–2021) monitoring of Asian golden cats in the Yarlung Zangbo Grand Canyon National Nature Reserve, Tibet, using camera traps at 283 points over 89,991 camera days. A total of 620 cat photos were recorded, including 344 (55.48%) with recognizable color patterns. Vector graphics of the coat patterns were extracted from the field image data, which revealed 10 color types in the ratio common: cinnamon: reddish-brown long hair: ocelot: blackening: melanistic: gray: brown: brown short hair: pure black = 123:76:57:35:22:8:7:7:5:4. The genes for coat pattern variation are widespread in the Asian golden cat population and are relatively stable. The increase in population size intraspecific competition has led to the tail break phenotype in individual cats. The gene encoding for tail breakage in Asian golden cats remains unknown. This study provides basic information for understanding faunal diversity in the Eastern Himalayan biodiversity hotspot and serves as a reference for studies on the formation mechanisms for feline color pattern diversity.

Color Variation and Habitat Use in Liolaemus silvai

Liolaemus is a species-rich genus endemic to South America with relatively little known about the biology of most of the > 200 included species. One species, L. silvai is common in the coastal Atacama Desert and is sexually dimorphic. We studied their phenotypic variation in color and body size, as well as habitat use by capturing lizards active on the surface. To assess phenotypic variation, we categorized the color morph of each lizard based on visible coloration in their ventral throat region and their ventral body from the shoulder girdle to the hips. We also sexed each lizard, measured snout–vent length and body mass, and recorded incidences of tail breakage. For habitat use we measured perch height, distance from the rock edge to nearest vegetation, and the height of the rocks on which lizards were initially sighted. We assessed habitat selection by comparing perch characteristics to features available in the habitat by pairing capture rocks with the nearest rock in a random direction from the initial perch site. Male L. silvai were significantly larger than females, but color morph and tail break frequency were independent of sex. Lizards used rocks that were significantly closer to vegetation than random rocks available in the environment independently of sex or color morph. We document the same pattern for perch height. Future studies are needed to examine the exact role of vegetation for L. silvai.

Tail breakage and predatory pressure upon two invasive snakes (Serpentes: Colubridae) at two islands in the Western Mediterranean

Tail breakage is an important anti-predator mechanism in snake populations, which can be used as a proxy for predation intensity as natural observations of predator-prey interactions are scarce. Frequency of tail breakage was calculated for two Iberian colubrids recently introduced in the Balearic Islands (Western Mediterranean, Spain): Hemorrhois hippocrepis (Linnaeus, 1758) in Eivissa and Zamenis scalaris (Schinz, 1812) in Formentera. The effect of sex, life-stage, dorsal coloration pattern, body length and body condition on frequency of tail breakage and on remaining subcaudal scale pairs (SBC) were analyzed and compared between the native range and the invaded islands. An increase of the frequency of tail breakage with body size was found, supporting a size-related effect, which also occurs in the native range. Frequency of tail breakage of H. hippocrepis was lower in Eivissa when compared with the original area, while in Formentera Z. scalaris showed a higher frequency, which could be related to the different predator community on each island compared with the mainland. The study of the main ecological aspects of these recent introduced species may allow to assess their potential impact on insular ecosystems and their native biodiversity as well as to promote future control actions in these areas previously free of snakes.

Assessing dairy cow welfare during the grazing and housing periods on spring-calving, pasture-based dairy farms.

The different periods characterizing spring-calving, pasture-based dairy systems common in Ireland have seldom been the focus of large-scale dairy cow welfare research. Thus, the aim of this study was to devise and conduct an animal-based welfare assessment during both the grazing and housing periods on spring-calving, pasture-based dairy farms, to identify areas for improvement and establish benchmarks for indicators of good welfare. Assessment of seven animal-based welfare indicators was conducted during two visits (one each at grazing and housing) to 82 commercial dairy farms in southern Ireland. Herd-level descriptive statistics were performed for all welfare indicators at each visit, and differences between visits were analyzed using paired t-tests and Wilcoxon signed-rank tests. A mean of 9% and 10% clinically lame cows (mobility scores 2 and 3) were observed at housing and grazing, respectively. Recommended body condition scores (BCS) were not met for a mean of 13% of cows at grazing and 23% at housing, with more over-conditioned cows present at housing than grazing (P < 0.001). Ocular discharge was uncommon in both periods. Prevalence of moderate and severe nasal discharge combined was lower during housing (5%) than grazing (7%). In both periods, similar mean levels of tail injury were observed: 2% to 3% of cows with tail lacerations, 9% with broken tails, and 8% (measured at housing only) with docked tails. Integument alterations involved primarily hair loss and were most prevalent on the hindquarters (26%) during grazing and on the head–neck–back (66%) and the hindquarter (32%) regions during housing. Cows displayed an avoidance distance of >1 m (indicative of a fearful response) from an approaching human in an average of 82% of grazing cows and 42% to 75% of housed cows, dependent on test location. Opportunities to improve welfare in this system were identified in the areas of tail injury prevention, nasal health, and the management of indoor housing and feeding. The performance of the top 20% of farms for each welfare indicator was used to establish benchmarks of: 0% to 5% clinical lameness, 0% to 12% of cows outside recommended BCS, 0% to 27% ocular discharge, 2% to 16% nasal discharge, 0% tail lacerations and docked tails, 0% to 3% tail breaks, 0% to 14% integument alterations, and 4% to 74% for avoidance distance of >1 m. These represent attainable targets for spring-calving pasture-based farms to promote good dairy cow welfare.

The Horseshoe whip snake (Hemorrhois hippocrepis) on Ibiza: predator release in an invasive population

Abstract The key to fighting a biological invasion may lie in understanding every variable that can explain its success. The Enemy Release Hypothesis (ERH) states that when an invader arrives to a new environment, the absence of its common enemies (predators, parasites and competitors) facilitates the invasion success. The Horseshoe whip snake (Hemorrhois hippocrepis) has been recently introduced from the Iberian Peninsula to the island of Ibiza, and it is currently threatening the only endemic vertebrate, the Ibiza wall lizard (Podarcis pityusensis). We hypothesized that the snake invasion success is caused by the absence of natural predators, and we checked the ERH by relating the tail breakage rate to predation pressure. The invasive population showed a much lower incidence of tail breakage than the source population, which is in agreement with the almost absence of snake predators among the Ibizan reduced and naïve native vertebrate community. These results confirm the ERH, and support the prolongation of invasive snake trapping campaigns.

A new tale of lost tails: Correlates of tail breakage in the worm lizard Amphisbaena vermicularis.

Predator–prey interactions are important evolutionary drivers of defensive behaviors, but they are usually difficult to record. This lack of data on natural history and ecological interactions of species can be overcome through museum specimens, at least for some reptiles. When facing aggressive interactions, reptile species may exhibit the defensive behavior of autotomy by losing the tail, which is also known as “urotomy”. The inspection of preserved specimens for scars of tail breakage can reveal possible ecological and biological correlates of urotomy. Herein, we investigated how the probability of urotomy in the worm lizard Amphisbaena vermicularis is affected by sex, body size, temperature, and precipitation. We found higher chances of urotomy for specimens with larger body size and from localities with warmer temperatures or lower precipitation. There was no difference in urotomy frequency between sexes. Older specimens likely faced – and survived – more predation attempts through their lifetime than smaller ones. Specimens from warmer regions might be more active both below‐ and aboveground, increasing the odds to encounter predators and hence urotomy. Probability of urotomy decreased with increased precipitation. Possibly, in places with heavier rainfall worm lizards come more frequently to the surface when galleries are filled with rainwater, remaining more exposed to efficient predators, which could result in less survival rates and fewer tailless specimens. This interesting defensive behavior is widespread in squamates, but yet little understood among amphisbaenians. The novel data presented here improve our understanding on the correlates of tail breakage and help us to interpret more tales of lost tails.

Does a Defensive Pseudoautotomy Mechanism Exist in the Subfamily Xenodontinae? A Study of the Genus Echinanthera

Pseudoautotomy is presumably a derived character within Lepidosauria and occurs in taxa that have lost the ability to perform autotomy. In general, species capable of employing pseudoautotomy as a defensive strategy against predators present a high frequency of damaged tails in series deposited in herpetological collections. We assessed data from three largely sympatric Echinanthera species in the Brazilian Atlantic Rainforest (E. cephalostriata, E. cyanopleura, and E. undulata) to test previous assumptions that species of Echinanthera use their tails defensively. This hypothesis derives from anecdotal observations during fieldwork and is reinforced by the number of specimens presenting tail breakage in scientific collections. In general, the frequency of damaged tails in these species resembles that of others in which pseudoautotomy has been demonstrated. Statistical analyses revealed no differences in tail breakage frequencies between sexes for the analyzed species or between the two geographical groups defined for E. cyanopleura. In contrast, we detected a significant difference between snout–vent length and sex regarding pseudoautotomy probability for E. cyanopleura, with a positive relationship between tail breakage frequency and snout–vent length.

Swimming improves platelet dysfunction in mice fed with a high-fat diet

Background We investigated the effects and mechanism of swimming on platelet function in mice fed with a high-fat diet. Material and Methods Mice were randomly divided into the control group (NC), high-fat group (HF), and high-fat diet combined with swimming group (FE). The FE group swam for 60 min a day, 5 days a week, for 8 weeks. Results Compared with the NC group, the HF group had significant weight gain, dyslipidemia, abbreviated bleeding time after tail breakage, increased clot retraction, increased platelet aggregation rate, increased spread of platelets on fibrinogen, and increased pAKT level in platelets. Compared with the HF group, the FE group had lower body weight, improved dyslipidemia, prolonged bleeding time, reduced clot retraction, reduced platelet aggregation rate, decreased spread of platelets on fibrinogen, and decreased pAKT level in platelets. Conclusions By inhibiting the level of pAKT in platelets, swimming improves platelet dysfunction in mice fed with a high-fat diet.

A Head/Tail Breaks-Based Method for Efficiently Estimating the Absolute Boltzmann Entropy of Numerical Raster Data

Shannon entropy is the most popular method for quantifying information in a system. However, Shannon entropy is considered incapable of quantifying spatial data, such as raster data, hence it has not been applied to such datasets. Recently, a method for calculating the Boltzmann entropy of numerical raster data was proposed, but it is not efficient as it involves a series of numerical processes. We aimed to improve the computational efficiency of this method by borrowing the idea of head and tail breaks. This paper relaxed the condition of head and tail breaks and classified data with a heavy-tailed distribution. The average of the data values in a given class was regarded as its representative value, and this was substituted into a linear function to obtain the full expression of the relationship between classification level and Boltzmann entropy. The function was used to estimate the absolute Boltzmann entropy of the data. Our experimental results show that the proposed method is both practical and efficient; computation time was reduced to about 1% of the original method when dealing with eight 600 × 600 pixel digital elevation models.

Curve Generalization Algorithm Based on Area of Bends using Head/tail Breaks

Abstract. For the early curve generalization algorithms, most of them only consider the reduction of the number of vertices, and do not take into consideration the important role of bends, especially the characteristic bends, on the shape of the curve. And the existing generalization methods based on the bends of the curve have complex algorithms and a large amount of calculation, focus on relationship between adjacent bends excessively and ignore the relationship among the overall bends. In addition, the threshold setting for filtering the bends is based on the unreasonable experience. Aiming at the problems above, a generalization algorithm based on the area of bends is proposed to achieve the purpose of simplifying the curve with the head/tail breaks classification method in this paper. Experiment shows that the algorithm is simple and efficient, and can iteratively take account of the overall bends with reasonable threshold, discarding the small bends and retaining the characteristic bends of the original curve to obtain generalization results which conform the natural law and is highly similar to the original graphics at different levels of detail.Head/tail breaks is a classification method that is always applied to the classification of heavy-tailed data. Heavy-tailed data is universal in nature and human society. For example, there are more small towns than big cities in the world. However, small towns are less important than big cities in the field of economy and politics. Thus, cartographers will mark the big cities on the map and eliminate the small town. Map generalization is a progress of retaining important elements and delete unimportant elements. Head/tail breaks is able to extract significant data which can be retained as a generalization result by arithmetic mean.Figure 1 shows the algorithm flow chart. First of all, we divide the curve into several bends with oblique-dividing-curve method. Secondly, we calculate the area of each bend, and then use head/tail breaks to complete the classification of the area of bends. If the percentage of bends in the head is less than 40%, it means the data conform to heavy-tailed distribution and can be classified with head/tail breaks. If the percentage of bends in the head is greater than 40%, the head/tail breaks is not applicable to this data. After classification, for the bends which is more important in the head, we reserve them directly. For the bends in the tail, we extract the feature points of each bend by retaining the point farthest from the axis so as to maintain the local shape of the original curve. Finally, we merge the bends in the head and the feature points as a generalization result.The experimental result is shown in the Fig 2. The data of this experiment is administrative division map of Gansu Province extracted from a China map with a scale of 1 : 10,000,000. Because algorithm can be executed iteratively, it can generate results at different levels of detail. We can see that from the result in detail to concise result, the graphic changes progressively and there is no oversimplified result. With comparison of three algorithms in the Fig 3, the generalization results of both this paper and bend group division algorithm have better retention of characteristic bends than Douglas-Peuker algorithm. However, the algorithm of this paper has higher compression ratio and less execution time than bend group division algorithm, as shown in Table 1.The algorithm of this paper is based on nature law rather than empirical threshold, and can generate progressive results at different levels of details by iteration. In addition, it takes overall relationship of bends into consideration, so the generalization result is unique. The experimental result shows this algorithm has not only better retention of characteristic bends than Douglas-Peuker algorithm but also higher compression ratio and less execution time than bend group division algorithm. To further optimize the algorithm, we will study how to evaluate the apparent extent of the curved feature better and how to extract and eliminate the small bend inside of the bend in the head in order to improve compression ratio in the future.

Abstract 412: 8p12 amplification pattern dictates FGFR1 dependency in squamous cell lung cancer

Abstract Squamous cell lung cancer (SQLC) is the second most common lung cancer subtype after adenocarcinoma and accounts for 30% of all lung cancer cases. However, in contrast to adenocarcinoma, SQLC lacks therapeutic targets like activating EGFR mutations, ALK or ROS translocations. Besides immune-checkpoint-inhibition a promising treatment option in SQLC is the recurrent amplification of the tyrosine kinase fibroblast growth factor receptor 1 (FGFR1) within the 8p12-p11 region. Thus, small molecules inhibiting FGFRs have been employed to treat FGFR1-amplified SQLC. However, only about 10% of such FGFR1-amplified tumors respond to single agent inhibitor therapy. To investigate the mechanism of FGFR inhibitor resistance in 8p12-p11 amplified SQLC we performed deep genomic and transcriptome sequencing on 53 FGFR1 amplified samples including primary tumors (n=33), patient derived xenografts (n=13) and cell lines (n=7). For 22 of these samples the response to FGFR inhibition was known. We detected frequent breaks within NSD3 (n=3), also known as WHSC1L1, favoring the expression of NSD3-short, which is known to enhance MYC expression. Furthermore, the amplification pattern for all samples was compatible with a breakage-fusion-bridge (BFB) mechanism, showing chromosomal telomeric losses, copy number, and frequent intrachromosomal head to head and tail to tail breaks. Genomic reconstruction of one sample suggests a tandem duplication followed by a BFB mechanism, implying that the BFB mechanism is a later event in tumor genesis. Intrachromosomal tail to tail fusions within a 400kb region close to the FGFR1 open reading frame, have been detected in 75% of patients with a partial response to FGFR inhibitor therapy (3 of 4 patients). A similar break was detected in the FGFR inhibitor sensitive cell line H1581. All samples, which responded to FGFR inhibition (n=9), demonstrated a centered amplification pattern on NSD3 / FGFR1 and excluded amplification of the adjacent disintigrin and metalloproteinase family members (ADAM) genes. In contrast, the main amplification peak of the non-responding samples (n = 13) was centered on ADAM family members, corresponding to an increase in ADAM expression. These data suggest strong relevance of these genes for tumor development and growth, and warrant further investigation. Citation Format: Florian Malchers, Martijn Henricus van Attekum, Martin Peifer, Roman Kurt Thomas. 8p12 amplification pattern dictates FGFR1 dependency in squamous cell lung cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 412.

The brown anole dewlap revisited: do predation pressure, sexual selection, and species recognition shape among-population signal diversity?

Animal signalling structures are amongst the most variable characteristics, as they are subjected to a diversity of selection pressures. A well-known example of a diverse signalling system in the animal kingdom is the dewlap of Anolis lizards. Dewlap characteristics can vary remarkably among and within species, and also between sexes. Although a considerable amount of studies have attempted to disentangle the functional significance of the staggering dewlap diversity in Anolis, the underlying evolutionary processes remain elusive. In this study, we focus on the contribution of biotic selective pressures in shaping geographic variation in dewlap design (size, colour, and pattern) and dewlap display behaviour at the intraspecific level. Notably, we have tried to replicate and extend previously reported results hereof in both sexes of the brown anole lizard (Anolis sagrei). To do this, we assembled a dataset consisting of 17 A. sagrei heterogeneous island populations from the Caribbean and specifically tested whether predation pressure, sexual selection, or species recognition could explain interpopulational variation in an array of dewlap characteristics. Our findings show that in neither males nor females estimates of predation pressure (island size, tail break frequency, model attack rate, presence of predatory Leiocephalus lizards) or sexual selection (sexual size dimorphism) could explain variation in dewlap design. We did find that A. sagrei males from larger islands showed higher dewlap display intensities than males from smaller islands, but the direct connection with predation pressure remains ambiguous and demands further investigation. Last, we could show indirect support for species recognition only in males, as they are more likely to have a ‘spotted’ dewlap pattern when co-occurring with a higher number of syntopic Anolis species. In conclusion, we found overall limited support for the idea that the extensive interpopulational variability in dewlap design and use in A. sagrei is mediated by variation in their biotic environment. We propose a variety of conceptual and methodological explanations for this unexpected finding.

Exploring body injuries in the horseshoe whip snake, Hemorrhois hippocrepis

Body injuries on snakes may serve as indices of predation rate, which is otherwise difficult to record by direct methods because of the usual scarcity and shy nature of these reptiles. We studied the incidence of body scarring and tail breakage in a Mediterranean colubrid, Hemorrhois hippocrepis , from south-eastern Spain. This species exhibits two traits that favour tail breakage, a long tail and active foraging tactics. The large sample (n = 328) of individuals acquired also enabled us to determine how the incidence of these injuries varies ontogenetically, between the sexes, in relation to energy stores, and to seek for the possible existence of multiple tail breakage. Overall, the incidence of tail breakage was rather low (13.1%) and similar to that of body scarring (12.7%). However, there was a significant ontogenetic shift in the incidence of tail breakage; such injuries barely appeared in immature snakes but stub-tailed individuals were present in 38.7% of snakes in the upper decile of body size. In contrast to most other studies, our data show a sex difference in the incidence of these injuries, adult male rates quadrupling those of adult females for body scarring and males maintaining larger stubs, probably because of the presence of copulatory organs housed in the base of the tail. Larger individuals did not have shorter tail stubs, a finding that does not support the multiple-tail-breakage hypothesis. Our results also fail to support the idea of a cost of tail breakage or body scarring in terms of body condition.

Unveiling a spatial tail breakage outbreak in a lizard population

Many ecological attributes of organisms vary spatially. This strict dependency upon space generally arises by individuals occupying places with the necessary resources and conditions for survival. For lizards, losing the tail is an evolved mechanism that allows them to escape predators or to avoid aggressive intraspecific agonistic interactions. We evaluated the spatial relation of tail loss in a population of the lizard Tropidurus montanus. Our results support the occurrence of a spatial cluster of autotomized lizards. However, we cannot relate the cluster formation to the crowding of neighbouring lizards nor to individuals’ body size. Tail loss in lizards is known to be related to predatory attacks or intraspecific aggression, and we now show that tail autotomy occurs in a non-random way regarding space, and thus is also related to the space occupied by individuals in populations.

Injured Salvator merianae (Teiidae) regenerates six tails in central Argentina

Lizards have the ability of regenerate many tissues like nerve cells, part of the mandible, parts of the limb, and most of them can regenerate the tail. Tail autotomy followed by tail regeneration is a strategy widely used in lizards to escape from predators. In some cases tail breaks but it does not detaches completely from the body, leading to a regenerated tail with multiple tips. Here we report the finding of a young individual of Salvator merianae from central Argentina which regenerated six tails after being injured.

A tale of lost tails: pseudoautotomy in the Neotropical snake genusDrymoluber(Serpentes: Colubridae)

Pseudoautotomy (no spontaneous tail breakage without regeneration) occurs in the snakes Drymoluber brazili (Gomes, 1918) and Drymoluber dichrous (Peters, 1863) throughout their geographic range. Examination of 197 specimens of D. dichrous and 60 D. brazili show, respectively, a frequency of tail breakage (FTB) in 26% and 40% of specimens, similar or higher than observed for most species with pseudoautotomy. There is no sexual difference in FTB for D. brazili, and no relationship between tail breakage and snout–vent length (SVL). For D. dicrous, tail breakage is more frequently observed in males when specimens are &lt;710 mm SVL, but for longer specimens, the FTB is higher in females; this strange pattern may not be explained by a single hypothesis. The FTB does not vary significantly between disjunct populations of D. dichrous, suggesting that they are subject to similar predation pressures and escape rates, or minor or no effect of habitat structure on predation risk. The FTB increases with SVL in D. dichrous (but not in D. brazili, probably due to sample size), which is an indication that as the snake grows, the chance of being injured increases and partial tail loss becomes an efficient defense. The multiple tail break hypothesis is not supported for the genus Drymoluber Amaral, 1930, remaining restricted to taxa with specialized pseudoautotomy.

The α-Subunit Regulates Stability of the Metal Ion at the Ligand-associated Metal Ion-binding Site in β3 Integrins

The aspartate in the prototypical integrin-binding motif Arg-Gly-Asp binds the integrin βA domain of the β-subunit through a divalent cation at the metal ion-dependent adhesion site (MIDAS). An auxiliary metal ion at a ligand-associated metal ion-binding site (LIMBS) stabilizes the metal ion at MIDAS. LIMBS contacts distinct residues in the α-subunits of the two β3 integrins αIIbβ3 and αVβ3, but a potential role of this interaction on stability of the metal ion at LIMBS in β3 integrins has not been explored. Equilibrium molecular dynamics simulations of fully hydrated β3 integrin ectodomains revealed strikingly different conformations of LIMBS in unliganded αIIbβ3 versus αVβ3, the result of stronger interactions of LIMBS with αV, which reduce stability of the LIMBS metal ion in αVβ3. Replacing the αIIb-LIMBS interface residue Phe(191) in αIIb (equivalent to Trp(179) in αV) with Trp strengthened this interface and destabilized the metal ion at LIMBS in αIIbβ3; a Trp(179) to Phe mutation in αV produced the opposite but weaker effect. Consistently, an F191/W substitution in cellular αIIbβ3 and a W179/F substitution in αVβ3 reduced and increased, respectively, the apparent affinity of Mn(2+) to the integrin. These findings offer an explanation for the variable occupancy of the metal ion at LIMBS in αVβ3 structures in the absence of ligand and provide new insights into the mechanisms of integrin regulation.

Density and distribution of cutaneous sensilla on tails of leopard geckos (Eublepharis macularius) in relation to caudal autotomy

The lizard tail is well known for its ability to autotomize and regenerate. Physical contact of the tail by a predator may induce autotomy at the location at which the tail is grasped, and upon detachment the tail may undergo violent, rapid, and unpredictable movements that appear to be, to some degree, regulated by contact with the physical environment. Neither the mechanism by which tail breakage at a particular location is determined, nor that by which environmental feedback to the tail is received, are known. It has been suggested that mechanoreceptors (sensilla) are the means of mediation of such activities, and reports indicate that the density of sensilla on the tail is high. To determine the feasibility that mechanoreceptors are involved in such phenomena, we mapped scale form and the size, density, distribution, and spacing of sensilla on the head, body, limbs, and tail of the leopard gecko. This species has a full complement of autotomy planes along the length of the tail, and the postautotomic behavior of its tail has been documented. We found that the density of sensilla is highest on the tail relative to all other body regions examined; a dorsoventral gradient of caudal sensilla density is evident on the tail; sensilla are more closely spaced on the dorsal and lateral regions of the tail than elsewhere and are carried on relatively small scales; and that the whorls of scales on the tail bear a one to one relationship with the autotomy planes. Our results are consistent with the hypotheses of sensilla being involved in determining the site at which autotomy will occur, and with them being involved in the mediation of tail behavior following autotomy. These findings open the way for experimental neurological investigations of how autotomy is induced and how the detached tail responds to external environmental input.