Interspecific Size Variation Research Articles

Scaling Relationships of Maximal Gape in Two Species of Large Invasive Snakes, Brown Treesnakes and Burmese Pythons, and Implications for Maximal Prey Size.

SynopsisSnakes are a phylogenetically diverse (> 3500 species) clade of gape-limited predators that consume diverse prey and have considerable ontogenetic and interspecific variation in size, but empirical data on maximal gape are very limited. To test how overall size predicts gape, we quantified the scaling relationships between maximal gape, overall size, and several cranial dimensions for a wide range of sizes (mass 8–64,100 g) for two large, invasive snake species: Burmese pythons (Python molorus bivittatus) and brown treesnakes (Boiga irregularis). Although skull size scaled with negative allometry relative to overall size, isometry and positive allometry commonly occurred for other measurements. For similar snout-vent lengths (SVL), the maximal gape areas of Burmese pythons were approximately 4–6 times greater than those of brown treesnakes, mainly as a result of having a significantly larger relative contribution to gape by the intermandibular soft tissues (43% vs. 17%). In both snake species and for all types of prey, the scaling relationships predicted that relative prey mass (RPM) at maximal gape decreased precipitously with increased overall snake size. For a given SVL or mass, the predicted maximal values of RPM of the Burmese pythons exceeded those of brown treesnakes for all prey types, and predicted values of RPM were usually least for chickens, greatest for limbed reptiles and intermediate for mammals. The pythons we studied are noteworthy for having large overall size and gape that is large even after correcting for overall size, both of which could facilitate some large individuals (SVL = 5 m) exploiting very large vertebrate prey (e.g., deer > 50 kg). Although brown treesnakes had longer quadrate bones, Burmese pythons had larger absolute and larger relative gape as a combined result of larger overall size, larger relative head size, and most importantly, greater stretch of the soft tissues.

Body size explains interspecific variation in size–latitude relationships in geographically widespread beetle species

1. In most birds and mammals, larger individuals of the same species tend to be found at higher latitudes, but in insects, body size–latitude relationships are highly variable.2. Recent studies have shown that larger‐bodied insect species are more likely to decrease in size when reared at increased temperature, compared with smaller‐sized species. These findings have led to the prediction that a positive relationship between body size and latitude should be more prevalent in larger‐bodied insect species.3. This study measured the body size of > 4000 beetle specimens (12 species) collected throughout North America. Some beetle species increased in size with latitude, while others decreased. Importantly, mean species body size explained c. 30% of the interspecific variation in the size–latitude response.4. As predicted, larger‐bodied beetle species were more likely to show a positive relationship between body size and latitude (Bergmann's rule), and smaller‐bodied species were more likely to show a negative body size–latitude relationship (inverse Bergmann's rule).5. These body size–latitude patterns suggest that size‐specific responses to temperature may underlie global latitudinal distributions of body size in Coleoptera, as well as other insects.

Composition of Bird Nests is a Species-Specific Characteristic

Bird nests represent an extended phenotype of individuals expressed during reproduction and so exhibit variability in composition, structure and function. Descriptions of nests based on qualitative observations suggest that there is interspecific variation in size and composition but there are very few species in which this has been confirmed. For these species, data of the amounts of different materials indicate that nest construction behaviour is plastic and affected by a variety of factors, such as prevailing temperature, geographic location, and availability of materials. The lack of data on nest composition is hampering our understanding of how nests achieve their various functions and how different species solve the problem of building a nest that will accommodate incubation and allow successful hatching of eggs. This study deconstructed nests of four species of the Turdidae, four species of the Muscicapidae, and six species of the Fringillidae and quantified the size of the nests and their composition. These data were used to test: (1) whether nest size correlated with adult bird mass; (2) whether it was possible to distinguish between species on the basis of their nest composition; and (3) whether, within a species, it was possible to distinguish between the cup lining and the rest of the nest based on composition. Most but not all nest dimensions correlated with bird mass. Principal component analysis revealed species differences based on nest composition and discriminant analysis could distinguish cup lining from the outer nest based on material composition. Intraspecific variation in composition varied among species and in general fewer types of material were found in the cup lining than the outer nest. These data provide insight into how nests are constructed by the different species and in conjunction with studies of the mechanical, thermal and hydrological properties of a nest, will begin to reveal how and why individual species select particular combinations of materials to build a nest.

Thesis Abstract Morphological and phylogeographic analysis of Brazilian tortoises (Testudinidae).

Thesis Abstract Morphological and phylogeographic analysis of Brazilian tortoises (Testudinidae).

Intra- and inter-specific variation in size and habitus of two sibling spider species (Araneae: Lycosidae): taxonomic and biogeographic insights from sampling across Europe

Discriminating closely related species can become a taxonomical challenge if a clear morphological diagnosis is lacking. Two subspecies have been recognized in Pardosa agrestis (Westring, 1861); however, their validity is still debated. To resolve this dilemma, quantitative and qualitative traits were measured for 30 females and 30 males per site from ten localities throughout Western Europe (11 measurements on each individual) and compared between subspecies. Mean annual temperature and geographical coordinates from all sites were also included in the statistical models in order to test for variations in size over the distribution range of each subspecies. We found significant differences in body size and size of copulatory organs as well as accurate criteria of discrimination between P. a. agrestis and P. a. purbeckensis F.O.P. Cambridge, 1895, suggesting that these taxa are two valid morphological species, occurring sympatrically. We also showed that temperatures did not directly influence the size of individuals, but that one species had smaller individuals at higher latitudes (following the converse Bergmann's rule), and that both species had larger individuals in centrally sampled populations (fitting to the centre hypothesis). © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113, 85–96.

Interspecific Variation in Size, Diapause Intensity, and Moisture Responses of First-Instar Speyeria (Lepidoptera: Nymphalidae) Larvae

Abstract Egg weights of Speyeria (Nymphalidae) species from California were measured to estimate relative sizes of first-instar larvae. First-instar larvae were compared for diapause intensity and for their physiological and behavioral responses to atmospheric humidity and free water. Diapause intensity, measured by number of days between first instar and molt to second instar, ranged from 7.6 d (Speyeria nokomis) to 40.7 d (Speyeria callippe). Among species, diapause intensity was uncorrelated with egg weight, but within three species (S. nokomis, Speyeria mormonia, and Speyeria zerene), diapause intensity was positively correlated to egg weight. There was significant interspecific variability in the desiccation tolerance of diapause larvae to low (11% RH) humidity. The least and most desiccation-tolerant species, respectively, were S. nokomis (LT50= 1.9 d) and S. callippe (LT50 = 13.6 d). Interspecific desiccation tolerance was uncorrelated with egg weight. Larvae of S. nokomis moved from lower to higher humidity within a humidity gradient, whereas larvae of S. callippe did not move toward higher humidity. Desiccated larvae of S. callippe and S. zerene rehydrated by imbibing free water. Exposure of S. callippe and S. zerene larvae to 100% RH in the absence of free water did not result in a body weight increase, but high humidity conditions reduced the rate of water loss.

Differential vulnerability to predation in two sympatric whelks is mediated by juvenile traits

AbstractIn many taxa, initial differences in offspring size play an important role in mediating subsequent performance; however, the consequences of interspecific variation in size for the performance of co‐occurring taxa have been rarely examined. We used the whelks Cominella virgata and C. maculosa, which co‐occur on rocky shores throughout their life cycles, to examine the vulnerability of early life‐stages to native predators under controlled laboratory conditions. Among all the predators evaluated (the cushion sea star Patiriella spp., the olive rockfish Acanthoclinus fuscus, the oyster borer snail Haustrum scobina, the smooth shore crab Cyclograpsus lavauxi, and the pebble crab Heterozius rotundifrons), hatchlings of both species (C. virgata: ~3 mm shell length [SL] and C. maculosa: ~1.5 mm SL) were especially vulnerable to the smooth shore crab Cy. lavauxi, the only potential predator in which mortality was greater than in the control treatment. Small shore crabs (~8 mm carapace width [CW]) were unable to eat hatchlings of either whelk species, whereas medium and large shore crabs (~12 and ~18 mm CW, respectively) consumed hatchlings of both prey species. Hatchlings of C. virgata were less vulnerable to predation by medium crabs than large ones, and those of C. maculosa were equally vulnerable to both sizes of crabs. In hatchlings of both prey species, shell length and shell thickness increased over time. Two months after hatching, only individuals of C. virgata had reached a size refuge from predation. Our results show that interspecific vulnerability to predators can be mitigated by larger sizes and thicker shells at hatching; nonetheless, our results also suggest that other species‐specific factors, such as juvenile growth rate, may also play key roles in determining the vulnerability of hatchling and juvenile snails to shell‐crushing predators.

Evolution of interspecific variation in size of attachment structures in the large tapeworm genusAcanthobothrium(Tetraphyllidea: Onchobothriidae)

Parasites have evolved a myriad of attachment structures closely adapted to their hosts and sites of attachment. Here, using members of the genus Acanthobothrium van Beneden, 1850 (Cestoda: Tetraphyllidea: Onchobothriidae), we (i) examined the influence of host body size and phylogeny, in addition to morphological features of these tapeworms, on the size of 3 structures used in attachment (bothridia, accessory suckers and hooks) by means of general linear models and phylogenetic-independent contrasts methods, and (ii) quantified the scaling exponents of relationships between size of attachment structures and tapeworm body size. Our results indicate that there exists a positive relationship, albeit not directly proportional, between size of attachment structures and Acanthobothrium spp. body size, and hook size and size of bothridia and accessory suckers. These results suggest that the resource investment in whole-body growth is greater than that in attachment structures, and that a greater investment in development of bothridia and accessory suckers is required to maintain an equivalent functional efficacy to hooks. In addition, host body size also influences, though less markedly, the size of attachment structures in Acanthobothrium spp. independently of parasite size itself. Acanthobothrium species have evolved a generalized mode of attachment that is successful in maintaining their position on various intestinal mucosal topographies across a variety of hosts exploiting different food resources.

An interspecific QTL study of Drosophila wing size and shape variation to investigate the genetic basis of morphological differences

The Drosophila wing has been used as a model in studies of morphogenesis and evolution; the use of such models can contribute to our understanding of mechanisms that promote morphological divergence among populations and species. We mapped quantitative trait loci (QTL) affecting wing size and shape traits using highly inbred introgression lines between D. simulans and D. sechellia, two sibling species of the melanogaster subgroup. Eighteen QTL peaks that are associated with 12 wing traits were identified, including two principal components. The wings of D. simulans and D. sechellia significantly diverged in size; two of the QTL peaks could account for part of this interspecific divergence. Both of these putative QTLs were mapped at the same cytological regions as other QTLs for intraspecific wing size variation identified in D. melanogaster studies. In these regions, one or more loci could account for intra- and interspecific variation in the size of Drosophila wings. Three other QTL peaks were related to a pattern of interspecific variation in wing size and shape traits that is summarized by one principal component. In addition, we observed that female wings are significantly larger and longer than male wings and the second, fourth and fifth longitudinal veins are closer together at the distal wing area. This pattern was summarized by another principal component, for which one QTL was mapped.

Scaling of the marsupial middle ear and its functional significance

AbstractThe marsupial middle ear performs an anatomical impedance matching for acoustic energy travelling in air to reach the cochlea. The size of the middle ear sets constraints for the frequencies transmitted. For generalized placental mammals, it has been shown that the limit for high‐frequency hearing can be predicted on the basis of middle ear ossicle mass, provided that the ears fulfil requirements of isometry. We studied the interspecific size variation of the middle ear in 23 marsupial species, with the following measurable parameters: skull mass, condylobasal length, ossicular masses for malleus, incus and stapes, tympanic membrane area, oval window area, and lever arm lengths for malleus and incus. Our results show that the middle ear size grows with negative allometry in relation to body size and that the internal proportions of the marsupial middle ear are largely isometric. This resembles the situation in placental mammals and allows us to use their isometric middle ear model to predict the high‐frequency hearing limit for marsupials. We found that the isometry model predicts the high‐frequency hearing limit for different marsupials well, indicating that marsupials can be used as auditory models for general therian mammalian hearing. At very high frequencies, other factors, such as the inner ear, seem to constrain mammalian hearing.

Responses of inoceramid bivalves to environmental disturbances across the Cenomanian/Turonian boundary in the Yezo forearc basin, Hokkaido, Japan

This paper describes the responses of inoceramid bivalves to events across the Cenomanian/Turonian boundary (C/T boundary), and the marine environments inferred from these responses, within the Yezo forearc basin, Hokkaido (northern Japan), as based on examination of newly collected specimens and a literature survey. All Late Cenomanian inoceramid species in this region became extinct at the C/T boundary and were replaced by newly evolved Early Turonian taxa. This change in generic composition, accompanied by stunting, a decrease in interspecific size variation, and predominance of cosmopolitan species evidently occurred immediately after the C/T transition. Based on these results and on previous studies, inoceramids would have been affected by oxygen-depleted conditions associated with Oceanic Anoxic Event 2. Consequently, niches became vacant in the Yezo forearc basin just after the C/T transition, and small, cosmopolitan species invaded those niches in the early Early Turonian. Faunal stunting suggests that oligotrophic conditions spread into the basin immediately after the C/T boundary.

Effects of climate on intra‐ and interspecific size variation in bumble‐bees

Summary In contrast to other social bees, bumble‐bees exhibit considerable size variation within the worker caste. This size variation has not been adequately explained, although it is known that larger workers tend to be foragers and smaller bees spend more time in the nest. We quantify size variation and mean size for foragers of 22 bumble‐bee species inhabiting climates ranging from arctic and montane to the lowland tropics. Mean size was larger in bee species from cold climates compared with temperate bumble‐bees. Within species, individuals from Scotland tended to be larger than those from southern England. However, tropical bumble‐bees (mostly belonging to the subgenus Fervidobombus) were largest of all. We suggest that although a lower limit to size may be imposed by inhabiting cold climates, overheating does not constrain large size in bumble‐bees from hot climates, perhaps because they have efficient mechanisms for heat loss through shunting heat to their extremities. Tropical bees had shorter thoracic setae than species from cooler climates, while B. terrestris from Greece had shorter setae than those from southern UK. Presumably shorter setae enhance heat loss in warm climates. Larger workers of B. terrestris were found to have smaller extremities, in proportion to their size, than small workers. We suggest that heat retention is more important in large bees that spend more of their time foraging, than in small bees which spend much of their time in the nest where incubation of the brood requires them to lose heat. In the temperate climate of southern UK, we found no evidence for ambient temperature having a differential effect on activity of workers of B. terrestris according to their size. We suggest that, at least in temperate climates, size variation in bumble‐bee foragers is probably not an adaptation to temperature variation. Instead it may improve colony foraging efficiency since foragers of different sizes are suited to, and tend to visit, different flower species.

Phylogenetic analysis of DNA length mutations in a repetitive region of the Hawaiiandrosophila yolk protein geneYp2

Nucleotide sequence analysis has demonstrated that interspecific size variation in the YP2 yolk protein among Hawaiian Drosophila is due to in-frame insertions and deletions in two repetitive segments of the coding region of the Yp2 gene. Sequence comparisons of the complex repetitive region close to the 5' end of this gene across 34 endemic Hawaiian taxa revealed five length morphs, spanning a length difference of 21 nucleotides (nt). A phylogenetic character reconstruction of the length mutations on an independently derived molecular phylogeny showed clade-specific length variants arising from six ancient events: two identical insertions of 6 nt, and four deletions, one of 6 nt, one of 12 nt, and two identical but independent deletions of 15 nt. These mutations can be attributed to replication slippage with nontandem trinucleotide repeats playing a major role in the slipped-strand mispairing. Geographic analysis suggests that the 15 nt deletion which distinguishes the planitibia subgroup from the cyrtoloma subgroup occurred on Oahu about 3 million years ago. The homoplasies observed caution against relying too heavily on nucleotide insertions/deletions for phylogenetic inference. In contrast to the extensive repeat polymorphisms within other Drosophila and the human species, the more complex 5' Yp2 repetitive region analyzed here appears to lack polymorphism among Hawaiian Drosophila, perhaps due to founder effects, low population sizes, and hitchhiking effects of selection on the immediately adjacent 5' region.

Chromosomal evolution withinPiperaceae

Chromosome numbers for 26 different species of the generaPiper, Peperomia andPothomorphe (Piperaceae) are reported. The basic chromosome numbers are 2n = 26, x = 13 (Piper, Pothomorphe) and 2n = 22, x = 11 (Peperomia), polyploid series are characteristic forPiper andPeperomia. Piper has the smallest chromosomes and prochromosomal interphase nuclei,Peperomia the largest ones and mostly reticulate to euchromatic nuclei.Pothomorphe is intermediate in both characters. The karyomorphological differences betweenPothomorphe andPiper underline their generic separation. Interspecific size variation of chromosomes occurs inPiper andPeperomia. Infraspecific polyploidy was observed inPiper betle. C-banding reveals different patterns of heterochromatin (hc) distribution between the genera investigated. The genome evolution is discussed.

Variations in Megastigmus from Rose Hips (Torymidae, Hymenoptera)

The two known species of Megastigmus from rose hips afford an unusually favorable group for a study of intraspecific and interspecific variation in size and color of the adults. They are very closely related (Milliron, 1949, p. 293), and have very similar habits and development, yet show striking differences as to the range of variation in size and color and also the numerical ratios of the sexes. The American form, Megastigmus nigrovariegatus Ashmead, and particularly the male, varies extremely in the percents of dark color, i.e., brown to black versus yellow pigmented areas on the body, and apparently comprises equal numbers of males and females. By contrast, the European species, M. aculeatus (Swederus), now known to occur also in Japan, China and the United States of America, shows, in my reared series, comparatively little range in color and size, and is predominantly female.