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Sexual dimorphism and allometry in the sphecophilous rove beetle Triacrus dilatus.

Marlowe MH, Murphy CA, Chatzimanolis S - PeerJ (2015)

Bottom Line: Linear regressions were run to examine if there were significant relationships between the different measurements.Our results indicated that males had significantly larger mandibles and ocular distances than females, but the overall body length was not significantly different between the sexes.We found no evidence of major and minor forms in either sex.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological and Environmental Sciences, University of Tennessee at Chattanooga , Chattanooga, TN , USA.

ABSTRACT
The rove beetle Triacrus dilatus is found in the Atlantic forest of South America and lives in the refuse piles of the paper wasp Agelaia vicina. Adults of T. dilatus are among the largest rove beetles, frequently measuring over 3 cm, and exhibit remarkable variation in body size. To examine sexual dimorphism and allometric relationships we measured the length of the left mandible, ocular distance and elytra. We were interested in determining if there are quantifiable differences between sexes, if there are major and minor forms within each sex and if males exhibit mandibular allometry. For all variables, a t-test was run to determine if there were significant differences between the sexes. Linear regressions were run to examine if there were significant relationships between the different measurements. A heterogeneity of slopes test was used to determine if there were significant differences between males and females. Our results indicated that males had significantly larger mandibles and ocular distances than females, but the overall body length was not significantly different between the sexes. Unlike most insects, both sexes showed positive linear allometric relationships for mandible length and head size (as measured by the ocular distance). We found no evidence of major and minor forms in either sex.

No MeSH data available.


Related in: MedlinePlus

Dorsal view of T. dilatus with measurements.Dorsal view of Triacrus dilatus showing the measurement of left mandible (A), ocular distance (B) and elytra length (C).
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fig-1: Dorsal view of T. dilatus with measurements.Dorsal view of Triacrus dilatus showing the measurement of left mandible (A), ocular distance (B) and elytra length (C).

Mentions: Specimens of T. dilatus are rather rare in museum collections, despite their relative large length (22–36 mm). We were able to borrow specimens from the following Natural History Museums, and even though this list in not exhaustive, it includes most specimens of Triacrus ever collected (Chatzimanolis, in press; numbers next to the acronym indicate how many specimens were used from each museum): Natural History Museum, London (BMNH, 13), Field Museum (FMNH, 15), Museum of Comparative Zoology (MCZ, 1), Naturhistorisches Museum Wien (MNW, 17), Finnish Museum of Natural History (MZH, 3) and the University of Tennessee at Chattanooga Insect Collection (UTCI, 2). Due to the specialized habitat of these beetles and their rarity, it was impossible to have specimens only from a single locality to control for geographic variation. To reduce any geographic bias we included all specimens that we were able to examine, including both sexes. Photographs (Fig. 1) were taken using a Visionary Digital Passport system with a Canon EOS 40D camera and Canon 50 mm and MP-E 65 mm macro lenses. We took photographs in multiple focal plains and then these images were automontaged using Helicon Focus 6.2.2 (http://www.heliconsoft.com/heliconsoft-products/helicon-focus/) to produce a single fully focused image. To establish a method of reliably referring to particular specimens, all specimens lacking unique identification numbers were given a UTCI barcode with a human readable number sequence. These barcodes do not establish ownership of specimens and they are simply used to associate particular measurements with a specimen.


Sexual dimorphism and allometry in the sphecophilous rove beetle Triacrus dilatus.

Marlowe MH, Murphy CA, Chatzimanolis S - PeerJ (2015)

Dorsal view of T. dilatus with measurements.Dorsal view of Triacrus dilatus showing the measurement of left mandible (A), ocular distance (B) and elytra length (C).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4525698&req=5

fig-1: Dorsal view of T. dilatus with measurements.Dorsal view of Triacrus dilatus showing the measurement of left mandible (A), ocular distance (B) and elytra length (C).
Mentions: Specimens of T. dilatus are rather rare in museum collections, despite their relative large length (22–36 mm). We were able to borrow specimens from the following Natural History Museums, and even though this list in not exhaustive, it includes most specimens of Triacrus ever collected (Chatzimanolis, in press; numbers next to the acronym indicate how many specimens were used from each museum): Natural History Museum, London (BMNH, 13), Field Museum (FMNH, 15), Museum of Comparative Zoology (MCZ, 1), Naturhistorisches Museum Wien (MNW, 17), Finnish Museum of Natural History (MZH, 3) and the University of Tennessee at Chattanooga Insect Collection (UTCI, 2). Due to the specialized habitat of these beetles and their rarity, it was impossible to have specimens only from a single locality to control for geographic variation. To reduce any geographic bias we included all specimens that we were able to examine, including both sexes. Photographs (Fig. 1) were taken using a Visionary Digital Passport system with a Canon EOS 40D camera and Canon 50 mm and MP-E 65 mm macro lenses. We took photographs in multiple focal plains and then these images were automontaged using Helicon Focus 6.2.2 (http://www.heliconsoft.com/heliconsoft-products/helicon-focus/) to produce a single fully focused image. To establish a method of reliably referring to particular specimens, all specimens lacking unique identification numbers were given a UTCI barcode with a human readable number sequence. These barcodes do not establish ownership of specimens and they are simply used to associate particular measurements with a specimen.

Bottom Line: Linear regressions were run to examine if there were significant relationships between the different measurements.Our results indicated that males had significantly larger mandibles and ocular distances than females, but the overall body length was not significantly different between the sexes.We found no evidence of major and minor forms in either sex.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biological and Environmental Sciences, University of Tennessee at Chattanooga , Chattanooga, TN , USA.

ABSTRACT
The rove beetle Triacrus dilatus is found in the Atlantic forest of South America and lives in the refuse piles of the paper wasp Agelaia vicina. Adults of T. dilatus are among the largest rove beetles, frequently measuring over 3 cm, and exhibit remarkable variation in body size. To examine sexual dimorphism and allometric relationships we measured the length of the left mandible, ocular distance and elytra. We were interested in determining if there are quantifiable differences between sexes, if there are major and minor forms within each sex and if males exhibit mandibular allometry. For all variables, a t-test was run to determine if there were significant differences between the sexes. Linear regressions were run to examine if there were significant relationships between the different measurements. A heterogeneity of slopes test was used to determine if there were significant differences between males and females. Our results indicated that males had significantly larger mandibles and ocular distances than females, but the overall body length was not significantly different between the sexes. Unlike most insects, both sexes showed positive linear allometric relationships for mandible length and head size (as measured by the ocular distance). We found no evidence of major and minor forms in either sex.

No MeSH data available.


Related in: MedlinePlus