Total Burrow Length Research Articles

Chromosomal and ecological studies of freshwater crabs,Sudanonautes aubryi(H. Milne-Edward, 1853) (Brachyura: Potamonautidae) from Ile-Ife, Nigeria

AbstractFew works have reported on the cytogenetics and ecological preferences of West African freshwater crabs. In this study, the chromosomal number, carapace dimensions, and ecological preference of 71 individuals of freshwater crab, Sudanonautes aubryi collected from a humid tropical rainforest region, Ile-Ife, south-western Nigeria were reported. Meiotic chromosomes from the ovotestes of an adult male were found to be metacentric and acrocentric with haploid number n = 33. Morphometric relationships between carapace dimensions (length, height, width, and frontal width) across two sampling sites within the study area show positive correlation among body sizes (carapace length (CL)). A comparison of the mean carapace dimensions and proportions estimated in this study with published data shows no significance difference (p > 0.05). Estimation of burrow parameters such as total burrow length and diameter were found to vary among sampling sites and there was no relationship between the CL and burrow diame...

Size-Class and Sex Dependent Variations of Burrow Architecture of Fiddler Crab, Uca rosea (Tweedie, 1937) in Sundarbans

Excavation of burrows by fiddler crabs are a crucial component of functional dynamics in mangrove ecosystem. Eleven burrow characters of rosy fiddler crab Uca rosea (Tweedie) were compared between two biotopes in Indian Sundarbans, throughout the year. Substratum qualities and mean shore level were estimated monthly. Mean density and sex ratio was calculated. Multivariate analysis of variance revealed significant differences (P < 0.05) in burrow morphology in different size classes of the species and in different seasons. Nine out of eleven characteristics differed between male and female fiddler crabs including burrow diameter (mm), burrow volume (cm3), total burrow length (mm) and depth (mm), chamber diameter (mm), burrow neck height (mm) etc., being larger in males than in females. These can be attributed to the presence of large chelipeds in males. Although, the two sites were different regarding the substratum composition, percent organic carbon and organic matter content, soil pH and shore level, the burrow morphology of rosy fiddler crab followed a fixed pattern that did not change even in different habitat.

Assessment of short and long-term effects of imidacloprid on the burrowing behaviour of two earthworm species ( Aporrectodea caliginosa and Lumbricus terrestris) by using 2D and 3D post-exposure techniques

Adverse effects of agrochemicals on earthworms’ burrowing behaviour can have crucial impacts on the entire ecosystem. In the present study, we have therefore assessed short- and long-term effects on burrowing behaviour in the earthworm species Aporrectodea caliginosa and Lumbricus terrestris after exposure to a range of imidacloprid concentrations (0.2–4 mg kg −1 dry weight (DW)) for different exposure times (1, 7, 14 d). 2D-terraria were used for the examination of post-exposure short-term effects (24–96 h), while post-exposure long-term effects were assessed by means of X-ray burrow reconstruction in three dimensional soil cores (6 weeks). For the latter each core was incubated with two specimens of L. terrestris and four of A. calignosa. Short-term effects on the burrowing behaviour (2D) of A. caliginosa were already detected at the lowest test concentration (0.2 mg kg −1 DW), whereas such effects in L. terrestris were not observed until exposure to concentrations 10 times higher (2 mg kg −1 DW). For both species tested in the 2D-terraria, “total burrow length after 24 h” and “maximal burrow depth after 24 h” were the most sensitive endpoints. 3D reconstructions of the burrow systems made by both earthworm species in the repacked soil cores revealed a significant linear decrease in burrow volume with increasing imidacloprid concentration. Since many of the observed effects occurred at imidacloprid concentrations relevant to natural conditions and since reduced activities of earthworms in soils can have crucial impacts on the ecosystem level, our results are of environmental concern.

Burrow morphologies of the ghost crabs &lt;i&gt;Ocypode ceratophthalma&lt;/i&gt; and &lt;i&gt;O. sinensis&lt;/i&gt; in foreshore, backshore, and dune subenvironments of a sandy beach in Japan

Burrow morphologies of the ghost crabs Ocypode ceratophthalma and O. sinensis were observed in foreshore, backshore, and dune subenvironments on the Irino Coast, southwestern Japan, with the aim of clarifying their paleoenvironmental significance. The observed diameter of the main shaft, burrow depth, and total burrow length varied from 14 to 40 mm, 12 to 89 cm, and 8 to 143 cm, respectively. Although the burrow diameters are largely similar among the three subenvironments, the burrows increased in length and complexity from the foreshore to dune subenvironments. These findings indicate that burrow morphology can be used as an indicator of ancient sandy beach subenvironments.

Effect of tunnel inclination on digging energetics in the tuco-tuco, Ctenomys talarum (Rodentia: Ctenomyidae)

Burrows play an important role for many species, providing them with shelter and access to food resources. For subterranean rodents, living underground imposes constraints on morphology and physiology. The convergence in burrow architecture among subterranean rodents has been related to the energy demands imposed by the cost of constructing an entire system. The low frequency of tunnels with downward angles steeper than 40 degrees appears to be a common feature in burrow design. In the subterranean habitat, movements through the soil are expensive and gravity can exert important restrictions on digging energetics when individuals push out the soil removed in steeper digging angles. The aim of this study was to determine the effect of digging angle on digging energetics in Ctenomys talarum. The mass of the removed soil and burrowing speed were similar while digging metabolic rate and net cost of transport were higher in individuals digging in tunnels with angles >40 degrees than in those digging tunnels with angles <40 degrees . The cost of constructing a burrow in the horizontal plane differed by 20% from others in which the natural representation of tunnels >40 degrees was considered. Even given that tunnels >40 degrees represented only 6% of the total burrow length, burrow architecture appears to be constrained by the high energetic cost of constructing in steeper angles.

Interspecific differences in the burrow morphology between the sympatric mud shrimps, Austinogebia narutensis and Upogebia issaeffi (Crustacea: Thalassinidea: Upogebiidae)

The morphology of burrows constructed by the upogebiid mud shrimps Austinogebia narutensis and Upogebia issaeffi was studied using resin castings of burrows in situ on Mukaishima Island, Seto Inland Sea, Japan, where the two species occurred sympatrically. The burrow structure of both shrimps is a relatively simple Y-shaped pattern, which is typical of the family Upogebiidae. Total burrow length, and length and overall width of the U-shaped section of A. narutensis were greater than those of U. issaeffi, possibly because A. narutensis is the larger species. When the ratios of the burrow measurements to the mean burrow diameter were compared to exclude possible size effects, the burrows of A. narutensis had a wider and shallower U-shaped section than those of U. issaeffi. Because the casts were made where the two species occurred sympatrically, the differences in the burrow morphology were not due to the differences in environmental factors but to the difference in the shrimp species, whether they are adaptive or not.

3D characterisation of earthworm burrow systems in natural soil cores collected from a 12-year-old pasture

To link earthworm burrow distribution with the spatial variability of soil functions, accurate mapping of their spatial burrowing patterns is required. Eight natural soil cores (25 cm in diameter; up to 60 cm long) were collected from a pasture in spring 2001–2003. Earthworm populations were sampled on the first date and the anecic species Nicodrilus giardi was found to be dominant (55% of the average density of 101 worms m −2). Soil cores were imaged using medical X-ray tomography equipment. These tomography images served as a basis for 3D reconstructions generated using specifically written software. Finally, the reconstructed burrow systems were measured and analysed using mathematical morphological approaches. The 3D reconstructions thus derived showed dense systems of interconnected burrows. A number of burrows extending vertically from the top to the bottom of the cores, but most were short, disconnected burrows. These two classes of burrows could not be linked with the activity of a particular species. In addition to the visual appraisal of the burrow system shape, structural parameters such as burrow volume, burrow wall surface area, burrow length density, topology and burrow angles were computed from the 3D reconstructions. Total burrow length density ranged from 687 to 1212 m m −3. Burrow volume density represented less than 2.5% of total soil volume and ranged from 13.3 × 10 3 to 24.2 × 10 3 cm 3 m −3. Inspite of the apparently high continuity of burrows, only 9–43% of the volume was connected to the soil surface. Total burrow wall area ranged from 7721 to 12764 cm 2 m −3 while surface-connected burrow wall surface area ranged from 1069 to 7237 cm 2 m −3. The drilosphere volumes (i.e. a 2 mm thick sheath around burrows) were estimated to range from 44.9 × 10 3 to 52.9 × 10 3 cm 3 m −3. Earthworm activity was found to vary throughout the year as revealed by changes in burrowing patterns. The burrow systems in spring 2001 were denser than that in others years, and the burrow systems in spring 2003 appeared to be partially re-filled close to the surface. This temporal variability demonstrates that it is virtually impossible to obtain true replicates of burrow systems of a given earthworm community without knowing (1) which burrows were created by which species and (2) the burrows age. However, the accurate description and quantification of earthworm burrow systems using powerful image processing tools allows a detailed discussion of the potential impact of earthworms on soil functions under natural conditions.

X-ray tomographic and hydraulic characterization of burrowing by three earthworm species in repacked soil cores

To test the assumption that different earthworm species make differently-structured burrow systems that can affect water permeability, the burrow systems made by adults of three earthworms species ( Lumbricus terrestris, Nicodrilus giardi and Octalasion lacteum) were studied in repacked soil cores (20 cm diameter by 40 cm high) under controlled conditions of temperature and humidity. Five core were used for each species and one adult earthworm was incubated per soil core over 21 days. Three-dimensional reconstruction (skeletons and volumetric images) of the burrow systems was performed and characterized after computer analysis of the 2D-slices from X-rays tomography. Total burrow length, number of burrows, branching rate, connectivity, burrow continuity, mean verticality and mean sinuosity of the burrows were measured from the skeletons. Differences were found between species in burrow characteristics: only one vertical and continuous burrow with large diameter for L. terrestris; long and complex burrow systems with branching burrows for N. giardi and O. lacteum. Moreover, 3D volume reconstruction of burrow systems enabled determination of the total volume, the distributed burrow volume as a function of depth and, using the tools of mathematical morphology, the pore size distribution of burrows. Results showed that the burrow volume of N. giardi was the highest; the three species had a unimodal pore size distribution centered on 8, 7 and 5 mm in diameter for L. terrestris, N. giardi and O. lacteum, respectively. Saturated hydraulic permeability was measured for each core and predicted using a water flow model. Significant differences between species were found, the burrow systems made by N. giardi being the most efficient for water flow. Differences in hydraulic properties between species resulted mainly from the difference in burrow continuity, the presence of openings at the soil surface and the burrow depth penetration.

DAILY MOVEMENTS AND MAXIMUM SPEED IN CTENOMYS TALARUM (RODENTIA: CTENOMYIDAE) IN ARTIFICIAL ENCLOSURES

Ctenomys talarum is a solitary subterranean rodent that maintains exclusive territories by constant movement through a sealed tunnel system. In this study we evaluate the distance traveled in an artificial burrow and maximum natural locomotor speed reached in a 24-h period. Distance moved per day was 179.99 m ± 69.62 SD, and ratio of distance moved to total burrow length was 12.4:1. Maximum locomotor speed was 0.75 m/s ± 0.01 SD. No relationships were found between either distance moved or speed and photoperiod or ambient temperature, and between body mass and distance moved or locomotor speed. Distance moved by C. talarum is related to maintenance of burrow and territorial defense, and locomotor speed, probably, responds to aboveground preation.

Evolution of burrow systems after the accidental introduction of a new earthworm species into a Swiss pre-alpine meadow

The unintentional introduction of a new earthworm species (Aporrectodea nocturna) into a Swiss pre-alpine meadow resulted in a great increase in earthworm density in the newly colonized area (386 m–2) compared with the density observed in the natural area (273 m–2) where an earthworm community was already present. To investigate the impact of this introduction on the burrow systems, eight soil cores (length 25 cm, diameter 16 cm) were taken (four in the colonized area and four in the natural area) and analysed with computer-assisted X-ray tomography. The resulting images were processed to obtain the 3D-skeleton reconstructions of the earthworm burrow systems. Due to high variability in these burrow systems, only slight differences were observed between the two areas. The total burrow length and the mean burrow lengths tended to be greater in the colonized area. Moreover, the distribution of pore numbers with depth showed different patterns with a maximum for depths between 10 cm and 15 cm in the colonized area and a maximum for depths between 20 cm and 25 cm in the natural area. These differences may have been related to: (1) the particular behaviour of A. nocturna, which was observed to cast at the surface in this site, and (2) the predominance of juvenile earthworms around the colonization front. These differences were sufficient to create significant effects on the continuity of the burrow systems (assessed by the number of different pathways between virtual horizontal planes) for the two areas. The colonized area was characterized by a greater pore continuity, which could have resulted in enhanced transfer properties.

3D skeleton reconstructions of natural earthworm burrow systems using CAT scan images of soil cores

Four soil cores (length, 20 cm; diameter, 16 cm) were sampled in a Swiss pre-Alpine meadow with high earthworm abundance (>400 individuals/m2); two cores were taken in October 1993 and the other two cores in April 1994. The cores were described using computer assisted tomography which gives a series of section images every 3 mm. A method for reconstructing the three-dimensional (3D) skeleton of the earthworm burrow system is presented and discussed. This method provides an image of the structural organisation of the burrow system and was found to be adequately sensitive for use in ecological and functional studies. The seasonal variation of these 3D skeletons was investigated using two approaches, i.e. the analysis of: (1) global burrow system characteristics, and (2) individual burrow characteristics. At the scale of the global burrow system no difference was found between seasons (same number of burrows and same total burrow length) except for the vertical segment distribution, which was homogeneous in spring and decreased with depth in the fall. The study of individual burrow characteristics revealed that burrows tended to be more vertical in spring and that their branching intensity was higher in this season.

Use of seagrass Zostera novazelandica (Setchell, 1933) as habitat and food by the crab Macrophthalmus hirtipes (Heller, 1862) (Brachyura: Ocypodidae) on rocky intertidal platforms in southern New Zealand

Along rocky reefs at Kaikoura, New Zealand, the crab Macrophthalmus hirtipes (Heller, 1862) constructs its burrows exclusively in patches of the intertidal seagrass Zostera novazelandica (Setchell, 1933). The occupation of seagrass patches is widespread, with 63% of patches having crab burrows. The number of externally visible burrows is highly correlated with the number of crabs inhabiting seagrass patches. Plaster casts of burrows revealed that burrows situated at the edge of seagrass patches differed from those away from the edge in having on average more entrances and passageways and, therefore, greater total burrow length. There was an average burrow density of 9.4 (± 1.04 S.E.) per m 2 of seagrass, but burrows were several times as numerous on the edges of patches, especially those that bordered tide pools. The diet of M. hirtipes was found to consist mostly of living seagrass (50.4 ± 3.40% of foregut contents) and sediment (39.2 ± 3.11% of foregut contents), with small amounts of isopods, amphipods and conspecifics also consumed. There were no intersexual or site-specific differences in diet. Ontogenetic differences in diet were found, with smaller crabs consuming more sediment and larger crabs consuming more seagrass. Crabs contributed significantly to erosion of seagrass patches. There was an average of 22.5% (± 5.27) loss of patch area where crabs were present compared to 1.8% (± 0.37) where crabs were absent from patches. Laboratory tests showed that burrow construction took around 250% longer in seagrass patches that had denser blade coverage. In the field, burrows persisted for up to 3 months, even if vacated by crabs. Their abundance at patch edges, combined with the loss of sediment and reduced binding of seagrass roots, accelerated erosion of seagrass patches.

Isopod miners in the leaves of two Western Australian Posidonia species

Isopods of the genus Lynseia have been found burrowing (leaf mining) in meadow forming seagrasses ( Posidonia) from Western Australia. These small (1.5–1.8 mm) isopods burrow beneath the epidermis consuming the mesophyll, forming a linear mine of similar width to the isopod along the leaf lamina. At Rottnest Island in January 1991, 75% of Posidonia australis Hook. f. and 66% of Posidonia sinuosa Cambridge and Kuo leaves were burrowed by isopods. Isopods were found in leaves of all sizes, but number of burrows, number of isopods and the length of burrows increased in older leaves. In P. australis, there were 3.15 ± 0.1 burrows and 2.6 ± 0.1 isopods per burrowed leaf, in P. sinuosa there were 2.9 ± 0.1 burrows and 2.48 ± 0.2 isopods per burrowed leaf. Isopods were mobile, vacating older burrows and forming new ones. Male and female isopods were found in pairs within burrows and young isopods were then brooded within the burrows, forming new branches from the parent burrow. Within monospecific stands of P. australis and P. sinuosa there were 2950 and 2280 isopods m −2 respectively. Mean length of individual burrows was 22 mm in P. australis and 28 mm in P. sinuosa. Total burrow length per leaf (mean ± SE) was 69.6 ± 3.6 mm in P. australis and 81.7 ± 4.7 mm in P. sinuosa. The consumption of leaf tissues and the resulting lines of weakness along burrow lines may have negative effects on the seagrass. Burrows facilitate entry of water, bacteria and fungi to the blade, leading to localised tissue death. Epiphytes may proliferate along burrow lines, owing to surface roughness or solute loss associated with the burrow. Burrows also split and increase fragmentation of leaves in storm events. Loss of photosynthetic area due to epiphytic growth and fragmentation of the leaves may reduce the growth of Posidonia. These potential effects of lynseid seagrass leaf miners may be important if the seagrass meadow was already under stress.

Semi-automatic image analysis of earthworm activity in 2D soil sections

A method is presented for quantifying various morphological changes of the soil fabric caused by earthworm activity. Adult earthworms were kept in planar glass cuvettes for 27 days (in one case for 45 days). The investigations were conducted with the endogeic species Aporrectodea caliginosa and the anecic species Aporrectodea longa. The distance between the glass sheets was suited to the diameter of the earthworms. This artificial, two-dimensional profile made possible the observation of the complete burrow system. The cuvettes were filled with sieved soil (aggregates of 1 to 2 mm diameter) so that morphological changes of the soil fabric could easily be detected. Photographs were taken of both sides of the cuvettes every 3 days forming a chronological series. For cast production and burrow system studies the photographs were analysed semi-automatically on a digitizing tablet with a morphometric programme. Cast production and total burrow length were greater in A. caliginosa compared to A. longa for the same period of time. Continuity of the burrows was also higher in A. caliginosa (60–70% of the total burrow length) than in A. longa (40–50%). In respect to the degree of reticulation of the burrows no difference between the two species was found.