Sexual Dimorphism In Tail Length Research Articles

Defensive tail displays in dice snakes (Natrix tessellata) are influenced by colour morph and sex

Abstract Defensive tail displays are common in squamates; however, the factors underlying the occurrence of such displays are rarely studied. We tested 268 adult dice snakes (Natrix tessellata) in a population with three colour morphs, exploring the effects of morph, sex, body size, tail length and temperature on the occurrence of tail waving in two stages of the antipredator response. When captured, the blotched morph tail waved the most, followed by melanistic then green morphs. Males displayed tail waving during post-capture immobility more often than females, possibly due to sexual dimorphism in tail length and/or fleeing speed. The occurrence of tail waving was low in response to a researcher as a “predator” (∼2.6% on capture; ∼6.8% during immobility), however the occurrence of this behaviour during encounters with real predators might be different. Large sample size is crucial for revealing fine scale effects on rare behaviours such as tail waving.

Correlated evolution of biparental incubation and sexual tail monomorphism in swallows and martins (Aves: Hirundinidae)

The evolution of sexually dimorphic ornamentation should reflect sex differences in a form of parental care, incubation behavior, but empirical support is scarce after controlling for phylogenetic inertia. Here, using phylogenetic comparative methods in swallows and martins (Aves: Hirundinidae), we studied the evolution of sexual dimorphism in tail length in relation to two incubation types, female-only and biparental incubation. We found that species with biparental incubation were more likely to have sexually monomorphic tails compared to species with female-only incubation. Furthermore, an analysis of evolutionary pathways suggested interdependent evolution of biparental incubation and sexual tail dimorphism; transitions to biparental incubation and sexual tail dimorphism were less likely to occur than transitions from that state. This finding is consistent with the hypothesis that selection on male ornamentation matters during the incubation period. We also confirmed that species with biparental incubation had significantly lower rates of extra-pair paternity compared to species with female-only incubation in this clade, providing additional support for the importance of selection on male ornamentation during the incubation period. The current study is one of few phylogenetic comparative studies demonstrating the correlated evolution of biparental incubation and sexual dimorphism in ornamentation.

Reproductive phenology in a Neotropical aquatic snake shows marked seasonality influenced by rainfall patterns

ABSTRACT Reproductive phenology of snakes varies widely among species, likely influenced by biotic and abiotic factors related to seasonality. In Neotropical regions, where seasonal variation in temperature and photoperiod is minimal, the factors regulating the reproductive phenology of snakes remain poorly known, despite the great diversity of species found in this region. We hypothesise that the phenology of tropical aquatic snakes is directly influenced by local precipitation patterns and resulting water levels. We studied for the first time the reproductive cycle of a neotropical aquatic oviparous snake, Helicops pastazae, in a mountain river in the Andean foothills of Colombia. To do so, we sampled 212 snakes from 2013 to 2017 and classified the monthly reproductive stages of the adult snakes. In females we observed follicular development and presence of oviductal eggs, in males we performed histological analyses of testes, kidney, and deferent ducts. Females showed a marked seasonal reproductive cycle, with secondary vitellogenic individuals mainly clustered during the high precipitation months, ovigerous stages found throughout low precipitation months, and with egg-laying occurring from low precipitation to the early dry seasons. Males produced spermatozoa throughout the year indicating year-round reproduction at a population level. We found sexual dimorphism in tail length, with both juvenile and adult males showing significantly longer tails than females, while adult females were larger than males and showed greater midbody width, head length, and head width. The reproductive activity of H. pastazae is highly seasonal in females, driven by regional rainfall patterns, whereas males are reproductive thorough the year, being a permanent resource for females.

Population diversity and relatedness in Sugarbirds (Promeropidae: Promerops spp.).

Sugarbirds are a family of two socially-monogamous passerine species endemic to southern Africa. Cape and Gurney’s Sugarbird (Promerops cafer and P. gurneyi) differ in abundance, dispersion across their range and in the degree of sexual dimorphism in tail length, factors that affect breeding systems and potentially genetic diversity. According to recent data, P. gurneyi are in decline and revision of the species’ IUCN conservation status to a threatened category may be warranted. It is therefore necessary to understand genetic diversity and risk of inbreeding in this species. We used six polymorphic microsatellite markers and one mitochondrial gene (ND2) to compare genetic diversity in P. cafer from Helderberg Nature Reserve and P. gurneyi from Golden Gate Highlands National Park, sites at the core of each species distribution. We describe novel universal avian primers which amplify the entire ND2 coding sequence across a broad range of bird orders. We observed high mitochondrial and microsatellite diversity in both sugarbird populations, with no detectable inbreeding and large effective population sizes.

Sexually dimorphic swallows have higher extinction risk.

The effect of sexual selection on extinction risk remains unclear. In theory, sexual selection can lead to both increase and decrease extinction probability depending on the ecology of the study system. Thus, combining different groups might obscure patterns that can be found in groups that share similar ecological features. Using phylogenetic comparative analysis, we studied sexual plumage dimorphism in relation to the perceived risk of extinction in hirundines (subfamily: Hirundininae), in which all species are socially monogamous aerial foragers. Among the 72 species studied, five species are facing a perceived threat of extinction. Species with sexually dimorphic plumage had a higher risk of extinction than did species with sexually monomorphic plumage. Likewise, when focusing solely on tail ornamentation, species that exhibit a sexual dimorphism in tail length had a higher risk of extinction than did other species. In Hirundininae, which are affected a great deal by severe weather, sexual selection and the resultant sexual dimorphism would increase extinction risk.

New insights into the systematics and molecular phylogeny of the Malagasy snake genus Liopholidophis suggest at least one rapid reversal of extreme sexual dimorphism in tail length

The pseudoxyrhophiine snake genus Liopholidophis Mocquard, 1904 (family Lamprophiidae) is endemic to Madagascar and according to its present definition comprises six medium-sized, terrestrial and diurnal snake species, most of which are characterised by an unusual and extreme sexual dimorphism in tail length. We performed molecular phylogenetic analyses using nucleotide sequences of three mitochondrial genes (16S rRNA, cytochrome b and cytochrome oxidase I) and one nuclear gene (c-mos) for all described and two additional species newly described herein. The two new species are very small sized (total length: 234–312.5 mm), have comparatively short tails and a reduced number of dorsal scale rows (15 at midbody), the lowest value among all non-scolecophidian snakes of Madagascar. Both species are secretive or rare, and they have a reddish belly in life that fades in preservative. In terms of colouration and morphology, they are most similar to each other and furthermore to Liopholidophis rhadinaea. Together with this species and L. dimorphus, they form a well-supported clade. Liopholidophis baderi sp. nov. from central eastern Madagascar is characterised by 149–158 ventrals and 71–77 subcaudals, whereas the similar L. oligolepis sp. nov. from the northeast has even fewer ventrals (137) and subcaudals (54). The phylogenetic tree suggests that the tail length dimorphism in the genus Liopholidophis has evolved in a complex pattern including at least one reversal. The phylogenetic position of the two new dwarf species indicates that both the absence of extreme sexual dimorphism in tail length and their body size reduction are derived and probably correlated features. Also the close phylogenetic relationships between the long-tailed L. sexlineatus and the similar but relatively short-tailed L. varius demonstrate that dimorphism in tail length can be strongly mitigated in short evolutionary time periods.

Ecology of the Snake Philodryas patagoniensis (Serpentes, Colubridae) from Northeast Argentina

We studied the sexual dimorphism, feeding habits, reproductive biology, and seasonal activity of the snake Philodryas patagoniensis in northeastern Argentina, where this species is the most abundant snake. There were differences in snout-vent length, tail length, and scale counts between adult males and females. Juveniles showed significant sexual dimorphism in tail length and scale counts. A total of 92 prey items was recorded from 184 specimens, with reptiles being the most common prey (58%) and Cercosaura schreibersii the most frequent individual prey item (26%). However, amphibians (15%), mammals (10%), and birds (4%) were taken occasionally. We found evidence of an ontogenetic diet shift because adults included endothermic prey. The female reproductive cycle was seasonal, and clutch size was positively correlated with female SVL. Philodryas patagoniensis was active throughout the year but significantly less so in winter and more so in spring. The great abundance of P. patagoniensis in South America may be influenced by its foraging and reproductive plasticity, feeding frequency, and the prey availability and abundance. Therefore, we suggest that this species may be an important predator in South American ecosystems.

Molecular phylogeny and systematics of the pseudoxyrhophiine snake genus Liopholidophis (Reptilia, Colubridae): evolution of its exceptional sexual dimorphism and descriptions of new taxa

The pseudoxyrhophiine snake genus Liopholidophis Mocquard, 1904 is endemic to Madagascar and consists of two distinct species groups. We performed molecular phylogenetic analyses using nucleotide sequences of c. 2200 bp from two mitochondrial genes (16S rRNA, cyt b) and one nuclear gene (c‐mos) to test the monophyly of the genus Liopholidophis and to investigate the relationships of the known species and an unidentified Liopholidophis population. Our phylogeny strongly supports the polyphyly of the genus Liopholidophis, confirms the monophyly of both species groups, and reveals that the unidentified population belongs to a new species. We therefore transfer the species of the former L. stumpffi group (L. epistibes, L. infrasignatus, L. lateralis, L. martae, and L. stumpffi) to a new genus Bibilava gen. n. and describe Liopholidophis dimorphus sp. n. from the rainforests of Montagne d’Ambre National Park in northern Madagascar. Finally, we compare our phylogeny with previous hypotheses and discuss the evolution of the extreme sexual dimorphism in tail length of Liopholidophis s. str.

Molecular phylogeny and morphological change in the Psittacula parakeets

We reconstruct a phylogeny of the African and Asian Psittacula parakeets using approximately 800bp of mitochondrial cytochrome b sequence to examine their evolutionary relationships in reference to their head plumage and major morphological tail innovations. Our phylogeny identifies three groups, whose distinctiveness is also apparent from their possession of three different head plumage characters: a neck ring, a distinctive colouration of the head, and a ‘moustache’-shaped pattern that extends from the chin to the cheek. We examine the extent of sexual dimorphism in tail length across the phylogeny and reveal large differences between closely related forms. We apply a range of published avian cytochrome b substitution rates to our data, as an alternative to internal calibration of a molecular clock arising from incomplete paleontological information. An ancestral Psittacula form appears to have evolved during the late Miocene-early Pliocene (3.4–9.7MYA), a time when regional geological processes on the Asian continent may have promoted subsequent diversity at the species level, and many forms diverged relatively early on in the evolutionary history of Psittacula (between 2.5 and 7.7MYA). However, others, such as the derbyan and moustached parakeets, diverged as recently as 0.2MYA. Our phylogeny also suggests that the echo parakeet from Mauritius diverged from the Indian ringneck parakeet as opposed to the African ringneck, and may have done so relatively recently. The molecular results indicate support for a southwards radiation from India across the Indian Ocean to Mauritius, where the arrival-date of the echo parakeet appears consistent with the island’s volcanic formation.

Evolution of the structure of tail feathers: implications for the theory of sexual selection.

Bird tails are extraordinarily variable in length and functionality. In some species, males have evolved exaggeratedly long tails as a result of sexual selection. Changes in tail length should be associated with changes in feather structure. The study of the evolution of feather structure in bird tails could give insight to understand the causes and means of evolution in relation to processes of sexual selection. In theory, three possible means of tail length evolution in relation to structural components might be expected: (1) a positive relationship between the increase in length and size of structural components maintaining the mechanical properties of the feather; (2) no relationship; that is, enlarging feather length without changes in the structural components; and (3) a negative relationship; that is, enlarging feather length by reducing structural components. These hypotheses were tested using phylogenetic analyses to examine changes in both degree of exaggeration in tail length and structural characteristics of tail feathers (rachis width and density of barbs) in 36 species, including those dimorphic and nondimorphic in tail length. The degree of sexual dimorphism in tail length was negatively correlated with both rachis width and density of barbs in males but not in females. Reinforcing this result, we found that dimorphism in tail length was negatively associated with dimorphism in tail feather structure (rachis width and density of barbs). These results support the third hypothesis, in which the evolution of long feathers occurs at the expense of making them simpler and therefore less costly to produce. However, we do not know the effects of enfeeblement on the costs of bearing. If the total costs increased, the enfeeblement of feathers could be explained as a reinforcement of the honesty of the signal. Alternatively, if total costs were reduced, the strategy could be explained by cheating processes. The study of female preferences for fragile tail feathers is essential to test these two hypotheses. Preferences for fragile tails would support the evolution of reinforcement of honesty, whereas female indifference would indicate the existence of cheating in certain stages of the evolutionary process.

EVOLUTION OF THE STRUCTURE OF TAIL FEATHERS: IMPLICATIONS FOR THE THEORY OF SEXUAL SELECTION

Bird tails are extraordinarily variable in length and functionality. In some species, males have evolved exaggeratedly long tails as a result of sexual selection. Changes in tail length should be associated with changes in feather structure. The study of the evolution of feather structure in bird tails could give insight to understand the causes and means of evolution in relation to processes of sexual selection. In theory, three possible means of tail length evolution in relation to structural components might be expected: (1) a positive relationship between the increase in length and size of structural components maintaining the mechanical properties of the feather; (2) no relationship; that is, enlarging feather length without changes in the structural components; and (3) a negative relationship; that is, enlarging feather length by reducing structural components. These hypotheses were tested using phylogenetic analyses to examine changes in both degree of exaggeration in tail length and structural characteristics of tail feathers (rachis width and density of barbs) in 36 species, including those dimorphic and nondimorphic in tail length. The degree of sexual dimorphism in tail length was negatively correlated with both rachis width and density of barbs in males but not in females. Reinforcing this result, we found that dimorphism in tail length was negatively associated with dimorphism in tail feather structure (rachis width and density of barbs). These results support the third hypothesis, in which the evolution of long feathers occurs at the expense of making them simpler and therefore less costly to produce. However, we do not know the effects of enfeeblement on the costs of bearing. If the total costs increased, the enfeeblement of feathers could be explained as a reinforcement of the honesty of the signal. Alternatively, if total costs were reduced, the strategy could be explained by cheating processes. The study of female preferences for fragile tail feathers is essential to test these two hypotheses. Preferences for fragile tails would support the evolution of reinforcement of honesty, whereas female indifference would indicate the existence of cheating in certain stages of the evolutionary process.

Tail Length and Mutual Mate Choice in Bearded Tits (Panurus biarmicus)

AbstractDirect sexual selection via mutual mate choice can result in both sexes showing conspicuous traits. We experimentally tested whether this hypothesis can explain tail length in the bearded tit (Panurus biarmicus). In this species, both sexes have a long, graduated tail. Males have, however, a longer tail than females, suggesting perhaps that females are choosier than males in selecting mates. We used two choice set‐ups for each sex: shortened vs. control tail individuals and elongated vs. control tail individuals. We found that direct sexual selection seems to operate differently in the two sexes. In both set‐ups, females spent more time with the male with the longest tail, and they also showed sexual display behaviour only towards these males. Males spent more time with control than with short‐tailed females, but they did not discriminate between control and long‐tailed females. Moreover, males displayed preference towards both short‐ and long‐tailed females. Thus, females preferred long‐tailed males, whereas males did not always prefer long‐tailed females. Our study suggests that mutual mate choice has played a role in the evolution of long tails in bearded tits. It also suggests that the sexual dimorphism in tail length has evolved because mate choice exerts a stronger sexual selection pressure on males than on females.

SEXUAL SELECTION AND TAIL-LENGTH DIMORPHISM IN SCISSOR-TAILED FLYCATCHERS

Abstract Scissor-tailed Flycatchers (Tyrannus forficatus) exhibit elongated tails in both sexes, and sexual dimorphism in tail length. At Fort Sill, Oklahoma, during 1991 and 1992, Scissor-tailed Flycatchers exhibited sexual dimorphism (male–female) in tail length (1.48), with more moderate sexual dimorphism in wing length (1.09) and beak length (1.04). Based on an analysis of museum specimens, immature birds (<1 year of age) of both sexes in their first calendar year exhibited significantly shorter tails than adults (measured in the field). Furthermore, tail length was highly variable among both sexes relative to other morphological traits. Male tail length was correlated with early clutch initiation by the male's mate and, in 1991, with larger clutch size. Similarly, female tail length was correlated with early clutch initiation, and, in one year, larger clutches. Longer-tailed females also tended to arrive earlier on the breeding grounds in 1992, the only year for which such data were available. Assort...

Sexual Selection and Tail-Length Dimorphism in Scissor-Tailed Flycatchers

AbstractScissor-tailed Flycatchers (Tyrannus forficatus) exhibit elongated tails in both sexes, and sexual dimorphism in tail length. At Fort Sill, Oklahoma, during 1991 and 1992, Scissor-tailed Flycatchers exhibited sexual dimorphism (male–female) in tail length (1.48), with more moderate sexual dimorphism in wing length (1.09) and beak length (1.04). Based on an analysis of museum specimens, immature birds (&lt;1 year of age) of both sexes in their first calendar year exhibited significantly shorter tails than adults (measured in the field). Furthermore, tail length was highly variable among both sexes relative to other morphological traits. Male tail length was correlated with early clutch initiation by the male's mate and, in 1991, with larger clutch size. Similarly, female tail length was correlated with early clutch initiation, and, in one year, larger clutches. Longer-tailed females also tended to arrive earlier on the breeding grounds in 1992, the only year for which such data were available. Assortative mating by tail length was observed. Those findings support the hypothesis that tail length is a sexually selected trait in this socially monogamous species, and that female tail length may be correlated with measures of female quality (e.g. early arrival and breeding, large clutches). However, confounding effects of age on tail length make it difficult to distinguish among various hypotheses for evolution of elongated tails in this species.

Sexual Selection and Exaggerated Male Tail Length in Birds

Many species of birds demonstrate extreme sexual dimorphism in tail length. Darwin's theory of sexual selection explained the evolution of such elaborate characters, arguing that selection is stronger under polygamy than under monogamy. Alternatively, R. L. Trivers proposed that relative parental investment was the key variable influencing sexual selection To determine whether tail length dimorphism is associated with mating system and/or relative parental care, we analyzed morphological information for 1,990 species and natural history information for 745 species. Controlling for phylogenetic effects by investigating associations within taxa, we found that tail length dimorphism was significantly associated with both mating system and relative parental care, but particularly with the latter. These results suggest that, when male birds invest less in parental care and/or are polygynous, selection for exaggerated male tail length is more likely to occur.

Aerodynamics and the evolution of long tails in birds

Two problems limit the interpretation of recent experiments1–3 supporting Darwin's4 suggestion that female choice for ornate males may account for the evolution of long tails in birds. First, in some species tail elongation may have been favoured by natural rather than sexual selection. Second, it is unclear how female preferences for elaborate males have evolved, because current tests of competing models are often inconclusive5–7. We have integrated aerodynamics theory with comparative data on sexual dimorphism in tail length to evaluate the flight costs of different forms of tail elongation. We report here that long tails with shallow forks are aerodynamically optimal, exhibit correspondingly low sexual dimorphism and may therefore have evolved under natural selection. Other long-tail types impair flight and show greater sexual dimorphism, but variation in their initial evolutionary cost suggests differences in how female preferences for them may have evolved.

Sexual dimorphism in wing and tail length as shown by the Swallow Hirundo rustica

In both sexes of Hirundo rustica two metric traits are significantly different. One of these traits, tail length, shows a positive correlation between mates and a negative correlation with the date of first egg laying. On the other hand, wing lengths are not significantly related in any of the corresponding tests. Similar relations were recorded both for all analysed birds and for at least two‐year‐old individuals. It is suggested that sexual selection, as proposed by Darwin (1871) for monogamous birds, is responsible for sexual dimorphism in the tail length of the Swallow. It seems that intersexual difference in wing length could be a result of such mechanisms as stabilizing the body sizes of males and females at different energetically optimum levels by natural selection.

Aspects of the Life History and Ecology of the Desert Night Snake, Hypsiglena torquata deserticola: Colubridae, in Southwestern Idaho

Aspects of the Life History and Ecology of the Desert Night Snake, Hypsiglena torquata deserticola: Colubridae, in Southwestern Idaho

The Adaptive Significance of Reversed Sexual Dimorphism in Tail Length of Woodpeckers: An Alternative Hypothesis

The Adaptive Significance of Reversed Sexual Dimorphism in Tail Length of Woodpeckers: An Alternative Hypothesis

Reversed Sexual Dimorphism in Tail Length and Foraging Differences in Woodpeckers

Reversed Sexual Dimorphism in Tail Length and Foraging Differences in Woodpeckers