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Larger Heads (larger + head)
Selected AbstractsDescription of a new Lake Tanganyikan cichlid fish of the genus Cyprichromis(Perciformes: Cichlidae) with a note on sexual dimorphismJOURNAL OF FISH BIOLOGY, Issue SB 2006T. Takahashi Cyprichromis coloratus, a new cichlid species, is described based on 41 type specimens from the Zambian coast of Lake Tanganyika. It differs from Cyprichromis microlepidotus by having fewer scales in the longitudinal line (41,44 v. 59,70 in C. microlepidotus) and upper lateral line (31,36 v. 47,59), from Cyprichromis leptosoma by more dorsal-fin spines (14,15 v. 11,13 in C. leptosoma) and longitudinal line scales (41,44 v. 38,40), from Cyprichromis pavo by fewer dorsal-fin spines and soft rays (29,31, usually 30, in total v. 30,32, usually 31, in C. pavo), and from Cyprichromis zonatus by shallower body depth [24·0,28·5 (26·4 ± 1·1)% of standard length v. 24·5,30·5 (28·4 ± 1·3)% in C. zonatus] and smaller eye [eye length 25·2,30·9 (27·2 ± 1·1)% of head length v. 27·9,33·3 (30·2 ± 1·2)%]. The new species is also separable from C. microlepidotus, C. pavo and C. zonatus by absence of distinct small spots on the body (v. pearl grey and yellowish small spots along scale rows on body at least in males of C. microlepidotus and C. pavo), its distinct dichromatism (particularly on the caudal fin) between males of the same population (v. dichromatism absent in C. zonatus) and absence of vertical bands (v. three or four distinct vertical bands beneath dorsal fin base in live males of C. zonatus). Cyprichromis coloratus n. sp. also exhibits sexual dimorphism, females having a larger head and males having longer pelvic fin, differences which are discussed in relation to reproductive behaviour. A key to the five species of Cyprichromis is included. A lectotype is designated for Cyprichromis leptosoma. [source] Ontogenetically stable dimorphism in a lacertid lizard (Acanthodactylus boskianus) with tests of methodology and comments on life-historyBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 2 2009MERAV SEIFAN Recent arguments in the literature prompted us to compare methods for assessing sexual dimorphism in body proportions of lacertid lizards, using Acanthodactylus boskianus. Although expressing body-part measurements as proportional to head length was the most effective method, we recommend using trunk length for the baseline as a general method for lizards. We also argue that, when aiming to assess sexual dimorphism in body proportions of lizards, if the context is ecological, all available adults should be included. However, for morphology and taxonomy, small sub-samples of the largest individuals that maximally express their genetic morphological potential should be used. In A. boskianus, the sexual dimorphism of mensural characters in adults was typical: males were larger, with relatively larger head and appendages. However, the ontogeny of this dimorphism was unusual in that the differences existed already in youth and thereafter persisted isometrically. The sexual dimorphism of meristic characters was male-biased in numbers of femoral pores and of caudal vertebrae, and female-biased in numbers of ventral plates along the trunk and of precaudal vertebrae. Size dimorphism may conceivably play a role in sex recognition because two potential visual cues (i.e. size dimorphism and dichromatism) appear to complement each other. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society 2009, 97, 275,288. [source] Relationships between head size, bite force, prey handling efficiency and diet in two sympatric lacertid lizardsFUNCTIONAL ECOLOGY, Issue 6 2002D. Verwaijen Summary 1Relationships between morphology, bite force capacity, prey handling efficiency and trophic niche were explored in two sympatric species of lacertid lizards, Podarcis melisellensis (Braun 1877) and Lacerta oxycephala Duméril & Bibron 1839. 2Head shape showed little variation, but head size (absolute and relative to snout,vent length, SVL) differed between species and sexes. Males have larger heads than females, both absolute and relative to their SVL. In absolute terms, male P. melisellensis have larger heads than male L. oxycephala, but the reverse case was true for the females. Relative to SVL, L. oxycephala have larger heads than P. melisellensis. 3Bite force capacity was estimated by having the lizards bite on two metal plates, connected to a piezoelectric force transducer. Differences in maximal bite force between species and sexes paralleled differences in absolute head size. Differences in body size and head size explain the higher bite force of males (compared with females), but not the higher bite force of P. melisellensis (compared with L. oxycephala). Among individual lizards, bite force correlated with body size and head size. 4Prey handling efficiency, estimated by the time and number of bites needed to subdue a cricket in experimental conditions, also showed intersexual and interspecific variation. This variation corresponded to the differences in maximal bite capacity, suggesting that bite force is a determining factor in prey handling. Among individual lizards, both estimates of handling efficiency correlated with maximal bite force capacity. 5Faecal pellet analyses suggested that in field conditions, males of both sexes select larger and harder prey than females. There was no difference between the species. The proportion of hard-bodied and large-sized prey items found in a lizard's faeces correlated positively with its bite force capacity. 6It is concluded that differences in head and body size, through their effect on bite force capacity, may affect prey selection, either directly, or via handling efficiency. [source] Sexual dimorphism of head morphology in three-spined stickleback Gasterosteus aculeatusJOURNAL OF FISH BIOLOGY, Issue 4 2010W. E. Aguirre This study examined sexual dimorphism of head morphology in the ecologically diverse three-spined stickleback Gasterosteus aculeatus. Male G. aculeatus had longer heads than female G. aculeatus in all 10 anadromous, stream and lake populations examined, and head length growth rates were significantly higher in males in half of the populations sampled, indicating that differences in head size increased with body size in many populations. Despite consistently larger heads in males, there was significant variation in size-adjusted head length among populations, suggesting that the relationship between head length and body length was flexible. Inter-population differences in head length were correlated between sexes, thus population-level factors influenced head length in both sexes despite the sexual dimorphism present. Head shape variation between lake and anadromous populations was greater than that between sexes. The common divergence in head shape between sexes across populations was about twice as important as the sexual dimorphism unique to each population. Finally, much of the sexual dimorphism in head length was due to divergence in the anterior region of the head, where the primary trophic structures were found. It is unclear whether the sexual dimorphism was due to natural selection for niche divergence between sexes or sexual selection. This study improves knowledge of the magnitude, growth rate divergence, inter-population variation and location of sexual dimorphism in G. aculeatus head morphology. [source] Life on a limb: ecology of the tree agama (Acanthocercus a. atricollis) in southern AfricaJOURNAL OF ZOOLOGY, Issue 4 2002Leeann T. Reaney Abstract One hundred and sixty-four museum specimens of the tree agama Acanthocercus a. atricollis were measured and dissected to examine sexual size dimorphism, reproduction and diet. Foraging mode and behaviour were also quantified in a wild population to obtain a broader picture of their foraging ecology and to test the hypothesis that tree agamas are ambush foragers. Males and females did not differ significantly in snout,vent length (SVL) or tail length; however, mature males had larger heads than females of the same body size. The smallest female showing sexual maturity was 96 mm SVL and the smallest male was 82 mm SVL. Mean clutch size was 11.3 and was positively correlated with female body size. Reproduction was seasonal and male and female reproductive cycles were synchronous. Testicular volume was greatest during August,September and females contained enlarged follicles during August,December and showed no evidence of multiple clutching. Tree agamas fed on a broad spectrum of arthropods (10 orders), including millipedes, which other lizard taxa have been reported to avoid. Gut contents were dominated numerically by ants (92%), followed by beetles (4%). Volumetrically, orthopterans (26.8%) were most important, followed by beetles (26.3%) and ants (17.9%). Compared to adults, juvenile diet by volume was dominated by ants and consisted of fewer large prey items (e.g. beetles and orthopterans). Seasonal effects in both prey diversity and volume were evident. Tree agamas are classic ambush foragers. They spent only 4% of their time moving and made few movements per minute (mean = 0.4). When stationary, adult tree agamas positioned themselves on tree trunks (34.7%), on lateral branches (41.8%) and occasionally, on the ground (23.4%). No evidence of trophic partitioning (intraspecific niche divergence hypothesis) was found and field observations revealed that males defend territories and engage in combat. This supports the idea that selection may be favouring larger head size in males, as an outcome of male contest competition. [source] | ||||||||||