Tail Breaks Research Articles

Shape and motion of drops sliding down an inclined plane

We report experiments on the shape and motion of millimetre-sized drops sliding down a plane in a situation of partial wetting. When the Bond number based on the component of gravity parallel to the plane . When this velocity is increased by tilting the plate, the drops change their aspect ratio: they become longer and thinner, but maintain a constant, millimetre-scale height. As their aspect ratio changes, a threshold is reached at which the drops are no longer rounded but develop a ‘corner’ at their rear: the contact line breaks into two straight segments meeting at a singular point or at least in a region of high contact line curvature. This structure then evolves such that the velocity normal to the contact line remains equal to the critical value at which the corner appears, i.e. to a maximal speed of dewetting. At even higher velocities new shape changes occur in which the corner changes into a ‘cusp’, and later a tail breaks into smaller drops (pearling transition). Accurate visualizations show four main results. (i) The corner appears when a critical non-zero value of the receding contact angle is reached. (ii) The interface then has a conical structure in the corner regime, the in-plane and out-of-plane angles obeying a simple relationship dictated by a lubrication analysis. (iii) The corner tip has a finite non-zero radius of curvature at the transition to a corner, and its curvature diverges at a finite capillary number, just before the cusp appears. (iv) The cusp transition occurs when the corner opening in-plane half-angle reaches a critical value of about 45°.

Inter‐populational variation in the cost of autotomy in the metallic skink (Niveoscincus metallicus)

AbstractMany species of lizard use tail autotomy to escape from potential predators. While frequency of tail loss is an unreliable indicator of predation intensity it may enable inter‐populational comparisons of predation costs. This reasoning was applied to a study of the metallic skink Niveoscincus metallicus. A total of 368 lizards was sampled from across four populations to compare the frequency and position of tail loss and ultimately to examine whether the implications of tail autotomy differ between populations. The overall frequency of tail loss was 72%, although between populations the incidence of tail autotomy varied from 61.4% (Laughing Jack Lagoon) to 78.2% (Dynnyrne). No sexual differences were observed in the frequency of tail loss; however, the incidence of autotomy increased with age. The estimated position of tail loss did not vary between the sexes, although individuals from Dynnyrne experienced more proximal tail breaks than the other populations. This resulted in the predicted energetic cost of tail loss being significantly higher in the Dynnyrne population and, when combined with a high frequency of tail loss and relatively smaller body size, suggests that this population incurs relatively high costs as a result of autotomy. Overall, measures of tail loss in N. metallicus were found to be useful for examining inter‐populational variation in the cost of tail autotomy.

Distribution of energy reserves in a viviparous skink: Does tail autotomy involve the loss of lipid stores?

Abstract Caudal autotomy is an effective defensive strategy used by many lizards to facilitate escape during predatory encounters. However, it has several potentially severe consequences, including a range of energetic costs that are believed to result from the depletion of caudal lipid reserves during tail loss. In this study we examined the possible effect of caudal autotomy on the energetic reserves of a small viviparous skink, Niveoscincus metallicus (O'Shaughnessy 1874). Animals of each sex were collected on three occasions to assess the distribution of lipid stores. In addition, the frequency and position of naturally occurring tail breaks were determined. Both abdominal and caudal lipid stores are present in N. metallicus; however, caudal fat bodies comprise the majority (55–78%) of these fat reserves. Temporal variation in fat body mass, both abdominal and caudal, was evident. There was a significant relationship between the two fat stores, which was distorted in pregnant females, when relatively more fat was stored in the tail. Examination of the distribution of caudal fat in the tail revealed that the majority (90–95%) occurs within the proximal third of the tail. The remainder is located in the middle portion of the tail, with no reserves in the most distal tail section. During late pregnancy, females store relatively more fat closer to the body. The frequency of tail loss in a natural population of N. metallicus was extremely high (78%). Tail breaks were normally distributed along the length of the tail (i.e. most near the middle and fewer distal and proximal breaks). Thus there was a relatively high chance of some lipid depletion as a result of tail loss, but because 76% of breaks occur in the middle and distal thirds of the tail, there is a high probability that tail loss results in only minimal (i.e. <10%) lipid depletion. This is the first instance where both the energetic ‘value’ of the tail and the likelihood of lipid depletion during tail loss have been determined in a lizard. Overall, the combination of the aggregation of caudal fat reserves and position of naturally occurring tail breaks may enable N. metallicus to combine caudal fat storage and tail autotomy with minimal conflict.

Changes in Reproductive Investment following Caudal Autotomy in Viviparous Skinks (Niveoscincus metallicus): Lipid Depletion or Energetic Diversion?

The effect of caudal autotomy on reproductive investment in females of a viviparous skink, Niveoscincus metallicus, was investigated to examine the relative importance of lipid depletion and energetic diversion to this activity. Although abdominal fat bodies are present, this species stores most of its energetic reserves in the tail. Since caudal fat is preferentially aggregated toward the base of the tail, autotomy and lipid depletion may be mutually exclusive events. Reproductive consequences following tail loss associated with significant loss of caudal fat were compared with those following autotomy involving no fat loss in two groups of females: females that had lost their tail during their most recent vitellogenic period; and females in which tail loss had occurred in a previous reproductive season. Caudal autotomy during vitellogenesis resulted in a significant reduction in litter size, irrespective of the position of tail loss, suggesting that smaller litters were a consequence of the diversion of energetic resources from reproduction to tail regeneration, rather than the loss of fat reserves per se. However, offspring from mothers that experienced tail loss during vitellogenesis without associated loss of fat reserves were significantly larger in size (snout–vent length and mass) and had longer tails than those from any other group. We suggest that this was probably achieved through facultative placental transfer during gestation, although the possibility that more yolk was allocated to each egg cannot be discounted. Sprint speed and the size of abdominal fat reserves at birth and postnatal growth were not correlated with either recency of autotomy or the location of the tail break.

Changes in Reproductive Investment Following Caudal Autotomy in Viviparous Skinks (Niveoscincus metallicus): Lipid Depletion or Energetic Diversion?

The effect of caudal autotomy on reproductive investment in females of a viviparous skink, Niveoscincus metallicus, was investigated to examine the relative importance of lipid depletion and energetic diversion to this activity. Although abdominal fat bodies are present, this species stores most of its energetic reserves in the tail. Since caudal fat is preferentially aggregated toward the base of the tail, autotomy and lipid depletion may be mutually exclusive events. Reproductive consequences following tail loss associated with significant loss of caudal fat were compared with those following autotomy involving no fat loss in two groups of females: females that had lost their tail during their most recent vitellogenic period; and females in which tail loss had occurred in a previous reproductive season. Caudal autotomy during vitellogenesis resulted in a significant reduction in litter size, irrespective of the position of tail loss, suggesting that smaller litters were a consequence of the diversion of energetic resources from reproduction to tail regeneration, rather than the loss of fat reserves per se. However, offspring from mothers that experienced tail loss during vitellogenesis without associated loss of fat reserves were significantly larger in size (snout–vent length and mass) and had longer tails than those from any other group. We suggest that this was probably achieved through facultative placental transfer during gestation, although the possibility that more yolk was allocated to each egg cannot be discounted. Sprint speed and the size of abdominal fat reserves at birth and postnatal growth were not correlated with either recency of autotomy or the location of the tail break.

Sexual differences in caudal morphology and its relation to tail autotomy in lacertid lizards

We hypothesized that the presence of the forked hemipenes, and associated musculature, at the base of the tail in male lizards should constrain the capacity to autotomize the tail. Thus, this hypothesis predicts that the non-autotomous base of the tail should be longer in male than in female lizards. We tested this hypothesis in four species oflacertid lizards. Males have on average one to two non-autotomous vertebrae more than females, and the sexual difference in length of the non-autotomous tail base remains constant over the entire body size range. In addition, the first functional autotomy plane in males is usually located on, or is distal to, the vertebrae from which two hemipenial muscles take origin. These observations support the view that functional demands of the male intromittent organs impose constraints on the abilities of tail autotomy. In a natural population of Lacerta vivipara, the proportion of tail breaks that occurred at very short distances from the base was highest in females, indicating that the small sexual difference in length of the non-autotomous tail part is of functional significance. Total length of the tail was largest in males. This can be interpreted as a compensation for the decline in autotomy capacities at the tail base, such that the length of the autotomous part remains similar in both sexes.

The natural history of demodectic mites on the skin of the eyelid margin

AbstractBackground Demodectic mites can be readily studied on the eyelid margin.Methods This was undertaken by scanning electron microscopy of the skin of the lid margin of full thickness eyelid specimens obtained by surgery.Results The whole life cycle of Demodex folliculorum, including the egg, nymph and adult stages was observed by electron microscopy of this region. The tails of adult mites protrude from hair follicles and also lie close to eyelashes either singly or in groups.Conclusions The eyelid littoral appears to be a significant site for egg laying by demodectic mites, and both intact and broken eggs have been seen. At the other end of the life cycle when adult mites die the protruding opisthosoma develops cracks in the carapace and the tail breaks off. Spillage of abdominal contents occurs which can carry fungi and bacteria on to the skin surface. All stages of the parasite including numerous casts of the ecdysed carapace contribute to debris found on the skin surface of the eyelid.

Latitudinal Variation in Activity Season Mortality Rates of the Lizard Uta Stansburiana

It is often claimed that predation pressure on plants and animals increases toward the equator. Here I address the specific hypothesis that predation pressure is greater on lower latitude populations of the lizard Uta stansburiana. Standard mark—recapture techniques (10 997 captures of 5371 individuals) were used to estimate mortality rates for seven populations that lie along a transect of nearly 15° latitude (central Washington to extreme southeastern California, USA). Mortality was estimated for both the early (i.e., spring to summer) and late (i.e., summer to late summer or fall) portions of the activity season. As in previous studies of this species, I found that emigration was negligible for adult lizards. Thus, disappearance rates serve as reliable indices of mortality rates. Although predation is known to be a major source of mortality for populations of U. stansburiana, direct measurement (i.e., observation) of the demographic impact of predators is impractical. My strategy was to examine the potential demographic importance of mortality sources other than predation (e.g., senescence, physiological stress). If alternate sources of mortality can be shown to be of trivial importance, then overall mortality rates can be used to infer variation in predation pressure. To assess the importance of these mortality factors I examined variation in mortality within sites (e.g., among seasons, years, and individuals) in relation to data about the lizard (e.g., age, physical condition) and about their environment (e.g., recent precipitation). My results suggest that predation is the only source of activity season mortality that is of demographic importance for these populations. For example, I found no evidence that physiological stress was ever an important source of mortality. Lizards in relatively poor physical condition (i.e., those with small length—corrected mass) did not experience a greater risk of mortality, and survival actually increased during the presumably more stressful late activity season. Mortality rates were also depressed during a drought at one site, despite the poor physical condition of the lizards. Low mortality rates during the late activity season and during drought conditions probably reflect reduced activity of U. stansburiana and their predators. Reduced activity levels discourage predator—prey encounters. Because sources of mortality other than predation appear to be of trivial demographic importance, overall mortality rates can be used to infer relative predation rates. Accordingly, I examined latitudinal variation in mortality rates to address the hypothesis that predation pressure is greater on lower latitude populations of U. stansburiana. Daily mortality rates were not higher among southern populations. Even annual losses to predators do not appear to be greater among lower latitude populations. These results were surprising because U. stansburiana is one of the species for which predation pressure was thought to increase with decreasing latitude. Higher than expected mortality rates in the north may in part be due to longer daily activity periods among northern Uta and their predators. Interestingly, several indirect measures of predation intensity (e.g., tail break frequencies, measures of predator species richness) did increase significantly from north to south. Thus, these less direct measures of predation pressure yielded a misleading impression of latitudinal variation in predation pressure.

Relationships Between Pre-anal fin Length and Total Length of Roughhead Grenadier (Macrourus berglaxlacepede) in the Northwest Atlantic

Tail breakage and regeneration in grenadiers has hindered accurate measurement of their total lengths. In 1980, the Scientific Council of the Northwest Atlantic Fisheries Organization (NAFO) adopted anal fin length (from the tip of the snout to the base of the first anal fin ray) as the standardized length measurement for both roundnose and roughhead grenadier. Linear relationShips between total length and anal fin length (more properly called pre-anal fin length) are available for roundnose grenadier, but similar relationships for roughhead grenadier in the Northwest Atlantic have not been derived previously. Analysis of data collected in NAFO Div. 2J and 3K in 1978 and 1979 indicate that total length (TL) and pre-anal fin length (AFL) are highly correlated for roughhead grenadier. Unlike in roundnose grenadier, no significant differences were found between the relationships for males and females. The combined relationship is TL = 5.2320 + 2.3455 * AFL.

Observations on the natural history, present status, and conservation of the insular lizard Podarcis hispanica atrata on the Columbretes archipelago, Spain

The world range of the lizard Podarcis hispanica atrata is retricted to the Columbretes archipelago in the Mediterranean. We examined its actual distribution, abundance and some aspects of its natural history. Lizards were found in four islets (combined area c. 20 ha). Densities on the largest islet (13 ha) are high (> 600 lizards/ha), at least in favourable habitats. Population sizes on the smaller islets are extremely small (< 200 individuals). A considerable number of juvenile lizards was found in all populations. We report new information on body length distribution, sexual dimorphism, tail break frequency, escape behaviour, and diet composition. Recommendations for the conservation of this lizard and the improvement of its habitat are given and discussed in relation to landscape management programmes.

Tail break rate in the madeiran lizard (Podarcis dugesii)

In the madeiran lizard, Podarcis dugesii (Milne-Edwards, 1829) adult animals force juveniles to use pessimal habitats with few escape sites. Consequently, juvenile individuals in populations with a high density show the highest rate of tail breaks.

故障が生じた航空機の制御系の再構成について

Recently, scale, speed and other performances of aircraft have increased and improved. Especially the active control technolgy (ACT) has contributed much to the improvement of performances. Such sophisticated aircrafts operate very well, when all the functions are normal. However, once failures occur in the functions, their normal operations can not be guaranteed, and the accommodation of failures and assurance of safety may require very quick, accurate and complicated restoring operation far beyond human ability. In these circumstances, control systems which automatically restructure themselves to accommodate failures and restore safety and performances, are desired. In this paper, let us suppose that vertical tail is broken in some ways and all the control surfaces are hardover because of failure of the hydro-pressure system. In this case, we study first the effects of vertical tail break on dynamic characteristics of the aircraft and effectiveness of thrust control using optimal regulator. Next we design a restructurable control system which is composed of parameter identification and optimal regulator subsystems. These studies and designs are conducted through computer simulations using a model of a large scale transport (Boeing 747).

Reproductive Cycle and Embryonic Development of Nerodia taxispilota (Serpentes: Colubridae) at the Northeastern Edge of Its Range

The seasonal reproductive cycle of Nerodia taxispilota in southeastern Virginia resembles that of other temperate zone colubrids. Testes are small during AprilJune, largest in Aug. and then decrease in size during Sept.-Nov. Spermatozoa produced in late summer are stored in the vas deferens through winter and used the following spring. The female cycle is annual. Vitellogenesis occurs during April-early June, ovulation in late June and parturition early to mid-Sept. Fecundity increases with increasing female body size. Mean total clutch size is 33.9 and mean clutch size of full-term embryos is 28.0. Sequential stages of embryonic development are described. Males average significantly smaller than females. Percentage of tail breaks are about equal in both sexes, but adults have higher proportions of tail breakage than juveniles. Sex ratios do not differ significantly from 1:1; however, males predominate in autumn.

Frequencies of Broken Tails among Uta stansburiana in Southern Nevada and a Test of the Predation Hypothesis

Frequencies of broken tails among hatchling (1-4 months), yearling (7-12 months) and 2-year old Uta stansburiana (19-24 months) in southern Nevada were examined for the years 1966-1973. Frequencies among males and females in the two older age groups did not differ significantly. The frequency of broken tails in hatchlings (0.06) was lower than that in yearlings (0.30), which was, in turn, lower than that in 2-year old Uta (0.51). Break frequencies among yearlings varied from 0.26 to 0.37 in different years, while frequencies among 2-year olds varied from 0.33 to 0.64. These differences were not statistically significant. Among hatchling Uta, tail break frequencies ranged from as low as 0.029 (1971) to as high as 0.099 (1966), and differences between years were highly significant. Tail break frequencies in all age groups were analyzed in terms of spring densities of Uta and of an important predator (Crotaphytus wislizenii). Tail breaks in yearling and 2-year old Uta were not correlated with either density variable. Tail-break frequencies of hatchling Uta were significantly correlated with predator density (r = 0.88), and multiple regression analysis (with densities of both lizards as independent variables) yielded an R2 of 0.80. This is the first test of the tail break

Partial Length as a Replacement for Total Length in Measuring Grenadiers

The problem of tail breakage and regeneration in grenadiers instigated the initiation of studies to find a suitable partial length measurement as a replacement for the traditional total length measurement. Studies undertaken in 1978 and 1979 on roundnose grenadier, Coryphaenoides rupestris, indicated that the partial length mesurements, pre-anus length and anal-fin length, were highly correlated with total length. The anal-fin length was considered to be more practical than pre-anus length, as the latter is sometimes affected by distortion of the anus due to air-bladder expansion and extrusion of intestines when the fish are brought to the surface from deep water. Consequently, the Scientific Council of NAFO at its meeting in June 1980 adopted anal-fin length (tip of snout to base of first anal fin ray) as the standard for measuring roundnose and roughhead grenadiers.

Ecological Consequences of Foraging Mode

Desert lizards are typically either widely foraging or sit—and—wait predators, and these foraging modes are correlated with major differences in ecology. Foraging mode is related to the type of prey eaten by lizards. Widely foraging lizards in the Kalahari desert, the Western Australian desert, and the North American desert generally eat more prey that are sedentary, unpredictably distributed, and clumped (e.g., termites) or that are large and inaccessible (inactive scorpions) than do sit—and—wait lizards. In contrast, sit—and—wait lizards eat more prey that are active. Foraging mode also appears to influence the types of predators that in turn eat the lizards. For example, a sit—and—wait snake eats predominately widely foraging lizards. Crossovers in foraging mode thus exist between trophic levels. Widely foraging lizards may also encounter predators more frequently, as suggested by analyses of relative tail lengths; but tail break frequencies are ambiguous. Daily maintenance energetic expenditures of widely foraging lizards appear to be about 1.3—1.5 times greater than those of sit—and—wait lizards in the same habitats, but gross food gains are about 1.3—2.1 times greater. Widely foraging species also have lower relative clutch volumes, apparently in response to enhanced risks of predation. Foraging mode within one species varies with changes in food availability. Physiology, morphology, and risk of predation might generally restrict the flexibility of foraging mode. Because foraging mode constrains numerous important aspects of ecology, any general model of foraging velocity must be complex.

Dominance and competition in an herbivorous lizard

A study of social organization in an herbivorous lizard Ctenosaura hemilopha investigated the role of dominance in group member behavior. Attention focused on a very populous (16 ind.) colony to examine causes and effects of crowding with respect to competitive factors. Lizards were colonial, with a top-rank male, one or more adult females, and various subadults and juveniles. Top-rank males defended harems, with colonies female-biased (1:4 in focal colony). Dominance hierarchy was observed, with females more aggressive than males, except for the top-rank male. Group awareness facilitated adaptive responses to threatening dominants and predators. Strong correlations existed among individual size, rank, and aggression. Top-rank male aggressiveness was partly explained by harem defense. Food resource competition, which causes aggression in female insectivorous lizards, did not explain female C. hemilopha behavior. Response to predators, predator fecal pellet analysis, and tail break frequencies implicate crevice escape sites for predator avoidance as a prime controller of social and population structure in these lizards.

Ecological and Demographic Correlates of Injury Rates in Some Bahamian Anolis Lizards

Raw tail-break frequencies in certain insular Anolis lizards are positively correlated with survival rates. Estimated intensity of predation, on the other hand, negatively correlates with survival rate and is greater on islands with more predatory bird species and in more open habitats. Estimated efficiency of predation upon A. sagrei females is greater in open habitats than in forests. Males have higher per-unit-time injury rates (tail, front toes, back toes) than females in A. sagrei and A. distichus, but not in the less territorial A. angusticeps. Front-toe injury rates are on one of three islands positively correlated with conspecific density; this is a likely kind of injury to result from intraspecific interaction. Tail-break and back-toe injury rates are more frequently negatively correlated with conspecific density; they are perhaps more likely to result from predation, in which case the correlation may reflect a depressive effect of predation on population size. The fraction injured in a population increases regularly with body size. Such curves, corrected for differential growth rates so as to reflect age, show the opposite relation of injury rate to habitat type than do the body-size curves. Three Anolis species differ little in injury rates, but a fourth, A. carolinensis, has an unusually low number of tail breaks.

Inferring the Properties of Predation and Other Injury‐Producing Agents from Injury Frequencies

This paper analyzes how cumulative injury data in age—structured populations can be used to determine some properties of the injury—producing process, such as predation. If the injury—producing process is the only source of mortality or injury, raw frequencies of animals free from injury (e.g., tail breaks) are shown in a theoretical analysis to equal the efficiency of the injury—producing process (e.g., the fraction of predation attempts that result in death of the prey); they are not affected by the intensity of the injury—producing process. If alternate sources of mortality exist, this conclusion may still be approximately true unless those sources are large. If there exists alternative sources of injury that never result in death, raw frequencies of uninjured animals actually increase with increasing intensity of the process that produces both injury and death (e.g., predation). To estimate the intensity of the injury—producing and the per—unit—time rate of accumulating injuries in the simplest case, one needs both injury and survival frequencies. Formulae for these estimations are provided.

Intraspecific Variation in demography and Life History of the Lizard, Sceloporus Jarrovi, Along an Altitudinal Gradient in Southeastern Arizona

Mark—recapture studies were conducted on a low (1675 m) and high (2542 m) altitude population of Sceloporus jarrovi in southeastern Arizona, USA from 1973 through 1976. Average age—specific mortality rates differed between altitudes only in the 0—1 yr age class. The increased mortality of neonates are low altitude was correlated with an increased number of potential predators and a significantly greater frequency of natural tail—breaks. Tail—break frequency did not differ between sites for older age classes. Survivorship and age at maturity were greater at high altitude. Low—altitude females mature in their first reproductive season. Transfer of neonates between altitudes indicate that high—altitude females do not mature in their first season even if raised at low altitude. Age at maturity appears to be adaptively adjusted by the demographic environment. Fertility schedules indicate that °40% of the replacement of low—altitude populations results from reproduction by 1st yr animals. There was a greater variation in replacement rate and population size at low than at high altitude.