Terrestris Burrows Research Articles

Inferring the lifestyles of extinct Crocodyliformes using osteoderm ornamentation.

Osteoderms are bony plates formed within the dermis of diverse vertebrate groups. They are present in all crocodylomorphs but Metriorhynchidae. Most of them show typical bone ornamentation consisting of pits and ridges on their outer surface. The most widely discussed functional hypothesis suggests that the ornamentation of osteoderms influences heat exchange with the environment through the adjacent vascular network, facilitating the absorption of solar radiation. This process allows semiaquatic crocodiles to compensate for heat loss resulting from the high thermal conductivity of surrounding water. In order to test this assertion, we conducted a phylogenetic logistic regression analysis to evaluate the relationship between osteoderm relative area of pits (RAP) and lifestyle (terrestrial versus aquatic) in a sample of crocodyliforms. Our results revealed that lifestyle is significantly explained by RAP: the lower the degree of ornamentation (RAP), the higher the probability of a terrestrial lifestyle. We used this model to infer the lifestyle of two extinct taxa, Peirosaurus torminni and Microsuchus schilleri. We concluded that terrestrial notosuchians may have lost osteoderm ornamentation due to the lower thermal conductivity of air and reduced heat loss in a terrestrial environment compared to what happens in water. Among these notosuchians, we hypothesize that large terrestrial baurusuchids maintained a stable body temperature due to thermal inertia, whereas small notosuchians took advantage of the early morning sun exposure to warm up and stayed in terrestrial burrows during periods of intense solar radiation. Finally, unlike the almost motionless behavior of freshwater crocodiles, fully marine Metriorhynchidae probably lost osteoderms because they constantly swim, generating heat by muscular contraction, so osteoderms with a thermoregulatory function for heat absorption were no longer positively selected.

Natural history and ecology of the slender crayfish (Faxonius compressus): an ecosystem engineer in the Western Highland Rim, USA

ABSTRACT Ecosystem engineers influence the physical environment, which changes the distribution and availability of resources to other organisms. Based on their burrowing abilities, freshwater crayfish have been widely recognised as ecosystem engineers. Crayfishes construct burrows that range from simple, rudimentary depressions in aquatic systems, to complex, labyrinth-like terrestrial burrows that may be significant distances from permanent water bodies. Here, we investigate ecosystem engineering and burrowing of the slender crayfish, Faxonius compressus, which lives in lotic environments characterised by an abundance of small cobble- and gravel-sized substrates. Without larger substrates to burrow under, we found F. compressus populations construct extremely high densities of burrows across riffle, run and pool macrohabitats. Based on the average number of burrows, a 5 × 100 m pool is estimated to contain an average of 25,860 burrows. We also conducted behavioural observations of this species to glean information on their natural history. Faxonius compressus regularly inhabits and competes for ownership of burrows which serve as a shelter from predators. Importantly, these burrows are not only used by F. compressus; we documented other crayfishes and fish species utilising these burrows. In total, we documented two other crayfishes and six fish species utilising F. compressus burrows. We discuss the ecosystem engineering abilities of this species in relation to other crayfish and suggest future avenues of research to elucidate this species’ natural and life history.

A multi-method approach for assessing the distribution of a rare, burrowing North American crayfish species.

Primary burrowing crayfishes face high extinction risk, but are challenging to study, manage, and conserve due to their difficult-to-sample habitat (i.e., terrestrial burrows) and low population densities. We apply here a variety of methods to characterize the distribution, habitat associations, and conservation status of the Boston Mountains Crayfish Cambarus causeyi (Reimer, 1966), an endemic burrowing crayfish found only in the Ozark Mountains of Arkansas, United States. We used species distribution modeling (SDM) on historic occurrence records to characterize the distribution and macro-scale habitat associations of this species. We then ground-truthed SDM predictions with conventional sampling, modeled fine-scale habitat associations with generalized linear models (GLM), and lastly developed and tested an environmental DNA (eDNA) assay for this species in comparison to conventional sampling. This represents, to our knowledge, the first successful eDNA assay for a terrestrial burrowing crayfish. Our MaxEnt-derived SDM found a strong effect of average annual precipitation on the historic distribution of C. causeyi, which occurred most frequently at locations with moderately high average annual precipitation (140-150 cm/yr) within our study region. Cambarus causeyi was difficult to detect by conventional sampling in 2019 and 2020, found at only 9 of 51 sites (17.6%) sampled by searching for and manually excavating crayfish burrows. Surprisingly, habitat suitability predicted from our MaxEnt models was not associated with contemporary C. causeyi occurrences per GLMs. Instead, C. causeyi presence was negatively associated with both sandy soils and the presence of other burrowing crayfish species. Poor SDM performance in this instance was likely caused by the omission of high resolution fine-scale habitat data (e.g., soils) and biotic interactions from MaxEnt models. Finally, our eDNA assay detected C. causeyi from six of 25 sites (24.0%) sampled in 2020, out-performing conventional surveys by burrow excavation for this species. Given the difficulty of studying primary burrowing crayfishes and their high conservation need, we propose that eDNA may become an increasingly important monitoring tool for C. causeyi and similar species.

Insect trace fossils as indicators of climatic conditions during the uppermost Pleistocene deposits in southern Brazilian Atlantic coast

AbstractThe Rio Grande do Sul Coastal Plain records sea-level oscillations driven by climatic changes during Quaternary glaciations, represented as four lagoon-barrier systems, the last one forming after the last glacial maximum and still active. Marine trace fossils are reported in the Pleistocene deposits, but terrestrial burrows also occur in the eolian deposits. The insect trace fossil assemblages from the uppermost Pleistocene deposits of the lagoon-barrier system III are used as relative proxies to infer the climate regimes that controlled sedimentation prior to the last glacial maximum. Two suites occur in the eolian deposits: the Vondrichnus suite, dominated by structures produced by termites, in the basal eolian beds; and the Celliforma suite, dominated by hymenopteran (bees and wasps) structures, in the upper eolian beds. The dominance of termite nests indicates humid conditions. The shift upward to the Celliforma suite signals a change in the humidity regime and the prevalence of drier conditions. The stratigraphic position of the ichnoassemblage, above the uppermost Pleistocene marine transgressive beds that formed during the last interglacial and below the record of the last glacial maximum in this coastal plain, suggests that the last glacial interval controlled this humid-dry fluctuation.

Prey and Predator Behavioral Interactions with a Primary Burrowing Crayfish (Lacunicambarus thomai)

Burrowing crayfish represent a small, specialized group of crayfish that inhabit self-made terrestrial burrows. Primary burrowing crayfish depend upon their burrows for protection, respiration, rearing of young, food storage, and thermoregulation. Burrowing crayfish tend to stay in proximity to or around their burrows causing them to be elusive lifestyle and consequently poorly documented. All crayfish are opportunistic generalists regarding food and have been recorded eating detritus, periphyton, and small invertebrates. Due to their stygobitic lifestyle, food resources are also limited to what is near their burrow, which commonly includes vegetation as well as smaller invertebrates. The predatory behaviors of burrowing crayfish has been studied and observed in abundance in epigean crayfish, however, it has been rare and few studies have been conducted on this behavior in burrowing species. This study utilized 24-h surveillance of a burrowing crayfish species, the Little Brown Mud Bug (Lacunicambarus thomai). A total of 633 H of videos were recorded of 6 different crayfish at varying times for each individual. Predatory behaviors were observed on several organisms including ants, worms, spiders, and dragonfly naiads. Gut analysis was performed on 23 L. thomai from 4 separate populations confirming the findings of the video footage that, in all populations, both animal and vegetation were being consumed. This study suggested that a sit-and-wait predation behavior may be a far more common foraging behavior in burrowing crayfish than previously observed.

Introduced earthworm species exhibited unique patterns of seasonal activity and vertical distribution, and Lumbricus terrestris burrows remained usable for at least 7 years in hardwood and pine stands

It is difficult to obtain non-destructive information on the seasonal dynamics of earthworms in northern forest soils. To overcome this, we used a Rhizotron facility to compile 7 years of data on the activity of anecic (Lumbricus terrestris) and endogeic (Aporrectodea caliginosa complex) earthworms in two contrasting soil/plant community types. We hypothesized that L. terrestris burrows would be used for longer than a typical L. terrestris lifetime, and that the distribution and activity pattern of the two earthworm species would respond differently to changes in soil moisture and temperature. For 7 years we recorded earthworm distribution and activity state bi-weekly to a depth of 1.5 m, tracked L. terrestris burrows using images captured annually, and measured soil temperature and moisture. Activity and vertical distribution of earthworms was closely linked to earthworm species and soil temperature in the fall, winter and spring. Lumbricus terrestris typically remained active through the winter, whereas the A. caliginosa complex was more likely to enter an aestivation period. Activity of all earthworms decreased substantially in July and August when soil temperature was at its highest and soil moisture at its lowest for the year. Most L. terrestris burrows were used continuously and moved very little during the 7-year study, likely creating spatiotemporally stable hotspots of soil resources. The different patterns of response of these species to soil temperature and moisture suggests that endogeic earthworms are more likely than anecic earthworms to adjust activity states in response to climate change mediated shifts in soil moisture and temperature.

The drilosphere concept: Fine-scale incorporation of surface residue-derived N and C around natural Lumbricus terrestris burrows

Anecic (deep-burrowing) earthworms are important for soil biogeochemical functioning, but the fine-scale spatial range at which they incorporate C and N around their burrows (the drilosphere sensu stricto) needs to be investigated under realistic conditions. We conducted a field experiment to delimit spatially the extent to which soil around natural Lumbricus terrestris burrows is influenced biochemically. We placed plant litter dual-labelled with 13C and 15N stable isotope tracers on L. terrestris burrow openings and we measured residue-derived 13C and 15N in thin concentric layers (0–2, 2–4, 4–8 mm) around burrows with or without a resident earthworm. After 45 days, earthworms were significantly enriched in 13C and 15N as a result of feeding on the plant litter. At 0–5 cm soil depth, soil 15N concentrations were significantly higher around occupied than unoccupied burrows, and they were significantly higher in all burrow layers (including 4–8 mm) than in bulk soil (50–75 mm from burrow). This suggests that biochemical drilosphere effects of anecic earthworms, at least in the uppermost portion of the burrow, extend farther than the 2 mm layer assumed traditionally.

Structure of earthworm burrows related to organic matter of a constructed Technosol

Literature considering earthworms as a biological agent of Technosol functioning, especially those constructed in order to reclaim degraded areas (e.g. industrial wasteland), is scarce. The main objectives of the following work is: (i) to describe the structure of burrows produced by two different eco-morphological groups of earthworms in a constructed Technosol and (ii) to link their burrowing activity to Technosol organic matter transfers and carbon content in one-species and two-species combinations. For these purposes, the contributions of Lumbricus terrestris as an epi-anecic earthworm and Aporrectodea caliginosa as an endogeic one to such functioning aspects of a constructed Technosol, resulting from soil engineering processes (e.g. choice of proportions, parent materials) were assessed using laboratory microcosm experiments. The Technosol studied was composed of green waste compost, treated industrial soil and paper mill sludge. Earthworms were inoculated separately and together in the constructed Technosol over a period of 75days. Ultra-structural analysis of randomly selected burrows of the one-species treatments and the soil of the control treatment were sampled to describe their structure. Functional consequences on the organic matter in the Technosol were assessed by studying remaining surface litter mass, transfer of surface organic matter to depth and by measuring soil carbon content.At the ultrastructural scale, the burrowing activity of the two eco-morphological groups of earthworms locally modified the organo-mineral associations of the Technosol. Burrows presented a similar structure for both species, with a looser internal cutan including some organic elements and microbial activity tracks (closed to the lumen) and a compacted external mineral cutan (distant from the lumen). However, structural differences were observed between species. L. terrestris burrows contained a visible organo-mineral interface, resulting from the interface between the internal cutan, which was much more organic than for the A. caliginosa one, and the external mineral cutan. For L. terrestris, mucus was present as a large stratum visible between the interface and the external mineral cutan, whereas the mucus was scattered for A. caliginosa. Aggregation also differed between species. Even though both burrows presented some organo-mineral aggregates, plant organic matter particularly contributed to the aggregates for L. terrestris, whereas aggregation was essentially bacterial for A. caliginosa. As is the case for “natural soils”, these results confirmed the notions of i) “ecosystem engineers” in constructed Technosols, by demonstrating that earthworms create organo-mineral structures with a similar structure and ii) eco-morphological groups by distinguishing differences between these structures. At a larger scale (microcosm scale), L. terrestris buried significantly more surface organic matter into depth than A. caliginosa. However, almost no effect of either of the two earthworms (one-species and two-species treatments) on soil carbon content was noticeable.It is suggested that not enough soil carbon measures were made given the temporal and spatial scales of this experiment or earthworm effects may have been masked in the man-made soil built with materials with high initial carbon content. Although sometimes slight at the microcosm scale, differences suggested that earthworm combinations of dissimilar eco-morphological groups led to different effects on organic transfers and carbon content of the constructed Technosol. Developing knowledge about effects of soil fauna diversity in constructed Technosols using reliable tools (e.g. trait-based approaches) is required. It would better predict the effects of biological agents such as earthworms in soil engineering and in turn improve the ecological restoration of such Technosols.

Evaluation of a Crayfish Burrowing Chamber Design With Simulated Groundwater Flow

Abstract Crayfish are a highly diverse group of freshwater crustaceans with great ecological and economic importance. Many species construct terrestrial burrows within which they reproduce, overwinter, and/or avoid desiccation. Basic life-history and environmental tolerance information is still lacking for many species, particularly in regards to terrestrial portion(s) of their life cycle. In this paper we present and evaluate a design for a crayfish burrowing chamber that allows for experimental control of burrowing conditions, including substrate, groundwater height and flow, as well as direct observation of burrow construction and measurement of groundwater quality. Results of evaluation assays with Cambarus striatus, a widespread secondary burrower native to the southeastern United States show that chambers are amenable to studies examining burrowing behavior, survivorship, growth and water quality. Water table height was easily manipulated in chambers. Seepage rates were strongly affected by substrat...

Miocene vertebrate and invertebrate burrows defining compound paleosols in the Pawnee Creek Formation, Colorado, U.S.A.

Ichnofossils from two compound paleosols in the middle Miocene Pawnee Creek Formation (PCF) of northeastern Colorado, U.S.A., indicate a diverse soil ecosystem that included plants, invertebrates, and vertebrates. The 2–4 m thick paleosols are characterized by blocky textures, shallow depth calcareous horizons overlying silty bioturbated horizons, calcareous nodules, dense mats of fine (< 1 mm diameter) rhizoliths in the upper 750 mm, 5–10 mm diameter rhizoliths up to 3 m deep, and burrows 2–800 mm in diameter. PCF paleosols likely formed within a shrubland and grassland environment. Ichnofossils include backfilled burrows with chambers and cocoons; simple backfilled burrows; small-diameter boxworks; cylindrical burrow complexes; large, scratch-marked burrow networks; large downward spiraling burrows; large subhorizontal burrows; and gravel-filled tunnels and chambers. These unique PCF ichnofossils include three new ichnogenera and eight new ichnospecies. Ichnofossils attributed to ground beetles, ants, reptiles, and mammals represent a complex variety of behaviors including temporary to permanent dwelling, nesting, and food storing. Rhizoliths and burrows used to interpret media consistency, organic content, soil moisture, and water-table level are tiered from shallow, intermediate, to deep levels within paleosols with respect to physical and biological factors. Separate bioturbated intervals permits the recognition of two different paleosols that otherwise might not have been recognized. Such well-developed paleosols with high densities of terrestrial burrows have substantial sequence stratigraphic significance since they define surfaces of low sedimentation, base level, and accommodation. The PCF ichnofossil assemblages represent at least three distinct ichnocoenoses. The Kladosystemites ichnocoenosis, with Kladosystemites, Polychoredrites, Parowanichnus, and 1–10 mm diameter rhizoliths, is present in the upper profile of well-drained, consolidated, and nutrient-rich paleosols with dense concentrations of small-to-large plants at the surface. The Beaconites ichnocoenosis, with Beaconites, Katarrhedrites, and 5–10 mm rhizoliths, is present in the lower profile of moderately organic paleosols above the influence of the water table but subject to seasonally variable saturated and unsaturated conditions due to precipitation. The Daimonelix ichnocoenosis, with Daimonelix, Beaconites, small-to-large Katarrhedrites, and 5–10 mm diameter rhizoliths, is present in the lower profile of very organic-rich paleosols generally above the influence of the water table but subject to seasonally variable saturated and unsaturated conditions. Integration of data from body fossils, ichnofossils, paleosols, and sedimentary environments provides new insight into Neogene ecosystems. Paleosol properties combined with the ichnofossil distribution, abundance, and diversity indicates that Miocene PCF paleosols formed under a seasonal climate subject to wide variation in temperature and precipitation. The diverse assemblage of burrow morphologies records adaptation of the local fauna to these environmental conditions. The response of soil ecosystems to short- and long-term changes in climate is, therefore, vital to any study of the effects of climate change in the geologic record.

Colony site choice of blue‐tailed bee‐eaters: influences of soil, vegetation, and water quality

All bee‐eaters (Family Meropidae) are cavity nesters, excavating terrestrial burrows in sites ranging from flat ground, to small mounds of soil, steep earthen banks seen in road clearings, eroded cliff faces, and river gorges. However, very little is known concerning the environmental factors that influence nest site selection in bee‐eaters. We addressed abiotic and biotic issues associated with colony site choice in blue‐tailed bee‐eaters (Merops philippinus) nesting on Kinmen Island, off mainland China, from 2000 to 2002. About 89% of the colonies were located on slopes with soils of sandy loam and the other 11% on sandy clay loam. No colony was found on clay loam, which covered 20% of the island. The sandy loam and sandy clay loam had lower soil pressure, density and moisture, which, presumably, were easier for bee‐eaters to excavate and provided better drainage and ventilation for nest cavities. Bee‐eaters avoided placing nest cavities in areas with dense vegetation and abandoned colony sites when they became overgrown. Vegetation would impede excavation and decrease the detectability of predators. Bee‐eaters may prefer colony sites near water bodies showing water chemistries indicative of more biological productivity, especially in relation to the diversity and abundance of their major prey, dragonflies.

Interaction of earthworm burrows and cracks in a clayey, subsurface-drained, soil

Installation of subsurface tile lines in poorly drained soils is a beneficial management practice that enhances crop productivity. In some instances, however, they can contribute to offsite losses of agricultural chemicals and sediment in drain flow. Movement of these materials through soil macropores (earthworm burrows and cracks) has been shown to contribute to this phenomenon. In order to determine if there was any interaction between these two types of macropores and subsurface drains we investigated water movement in a sandy clay field in southwest Finland that had 1 m-deep tile drains installed in the 1950s. Previous studies at this site suggested that cracks were important in terms of water movement and that Lumbricus terrestris L. populations were greater, and their burrows deeper, above the drains than in the area between drains. Mean infiltration rate for soil above the drains was twice that of the mid-drain position and the infiltration rates were positively correlated to L. terrestris numbers and biomass. Infiltration rates in individual L. terrestris burrows, measured with the plow layer removed to reduce the influence of cracks, ranged from 6 to 1043 ml min −1 (average 358 ml min −1) and did not appear to be related to the position of the burrows relative to the buried tile. Consistently higher infiltration rates (average 1080 ml min −1) were noted when measurements were made with the plow layer intact. Dye poured into the cracks adjacent to these burrows indicated water movement to the base of the plow layer, which acted as a hydraulic barrier, followed by lateral movement until open earthworm burrows were encountered. Water movement to the depth of the tile was exclusively in L. terrestris burrows with 106 dyed burrows m −2 observed 10 cm above the tile. These observations indicate that entry of water into this soil is probably dominated by cracks when it is dry enough for their formation, yet rapid movement of materials entrained by this flow to the subsurface drains depends on connection of the cracks to earthworm burrows.

Microbial and Microfaunal Community Dynamics in Artificial and Lumbricus terrestris (L.) Burrows

Macropore formation and litter incorporation are two results of earthworm [Lumbricus terrestris (L.)] activities that can influence trophic dynamics inside burrows. Thus, mesocosms were constructed to examine changes in microbial biomass and microfaunal communities inside artificial compared with earthworm burrows. Four treatments were established: (i) no worms (CTRL); (ii) unlined, artificial burrows (ARTF); (iii) corn (Zea mays L.) leaf litter‐lined, artificial burrows (LEAF); and (iv) Lumbricus terrestris (L.) burrows (WORM). There were no consistent differences in community structures between unlined, artificial burrows and control soils during a 16‐wk incubation. In contrast, protozoan numbers were elevated throughout the experiment in LEAF and WORM. A succession of nematode abundances occurred in LEAF, with plant parasitic and Tylenchid nematode numbers peaking at 5 wk, followed by high bacterivorous and fungivorous nematode numbers. In WORM, bacterivorous nematode numbers and active bacterial biomass were elevated for 1 and 3 wk, respectively, before declining. Active fungal biomass increased in WORM, whereas fungivorous nematodes were inhibited in earthworm burrows. While litter incorporation appeared to accelerate the rate of trophic interactions in artificial burrows, the effects of earthworms appeared to transcend that of litter translocation into soil, with earthworms differentially selecting for particular food web dynamics.

Microbial and Microfaunal Community Dynamics in Artificial and (L.) Burrows

Macropore formation and litter incorporation are two results of earthworm [Lumbricus terrestris (L.)] activities that can influence trophic dynamics inside burrows. Thus, mesocosms were constructed to examine changes in microbial biomass and microfaunal communities inside artificial compared with earthworm burrows. Four treatments were established: (i) no worms (CTRL); (ii) unlined, artificial burrows (ARTF); (iii) corn (Zea mays L.) leaf litter-lined, artificial burrows (LEAF); and (iv) Lumbricus terrestris (L.) burrows (WORM). There were no consistent differences in community structures between unlined, artificial burrows and control soils during a 16-wk incubation. In contrast, protozoan numbers were elevated throughout the experiment in LEAF and WORM. A succession of nematode abundances occurred in LEAF, with plant parasitic and Tylenchid nematode numbers peaking at 5 wk, followed by high bacterivorous and fungivorous nematode numbers. In WORM, bacterivorous nematode numbers and active bacterial biomass were elevated for 1 and 3 wk, respectively, before declining. Active fungal biomass increased in WORM, whereas fungivorous nematodes were inhibited in earthworm burrows. While litter incorporation appeared to accelerate the rate of trophic interactions in artificial burrows, the effects of earthworms appeared to transcend that of litter translocation into soil, with earthworms differentially selecting for particular food web dynamics.

DO NON-BREEDING, ADULT LONG-TOED SALAMANDERS RESPOND TO CONSPECIFICS AS FRIENDS OR AS FOES?

The majority of studies of amphibian sociobiology focuses on breeding individuals. However, adults certainly interact when not breeding and may do so subtly and in natural habitats that are inaccessible to direct observation. We conducted three laboratory experiments to explore social interactions among non-breeding, adult long-toed salamanders (Ambystoma macrodactylum columbianum), which reside in terrestrial burrows in nature. In substrate discrimination tests, salamanders preferred areas that bore chemical cues indicative of occupancy by a conspecific relative to clean areas (Experiment 1). However, only females discriminated occupant sex, preferring to associate with chemical cues derived from males (Experiment 2). When provided with a partner, salamanders spent more time in cohabitation in an artificial burrow than residing alone (Experiment 3). Our data suggest that, in nature, non-breeding adults may be social rather than territorial; conspecifics may aggregate rather than exclude one another. However, males and females may experience different kinds of benefits and costs to sociality outside of the breeding season, perhaps as a function of sex differences in energetic requirements for future reproduction.

Abundance of the earthworm Lumbricus terrestris in relation to subsurface drainage pattern on a sandy clay field

Subsurface drainage induces systematic spatial variability in soil properties which may be reflected in the abundance and distribution of soil organisms. We compared the population density of the deep burrowing earthworm Lumbricus terrestris L. above and between tile subdrains in 41 sample pairs on an eight hectare grass field. Above the drains the median number of individuals was twice as high and their total fresh mass five times as high as between the drains (4.5 vs. 2.1 individuals m -2 and 9.6 vs. 1.9 g m -2, respectively). The mean difference (above drain – between drains) was 2.5 individuals m -2 (95% CI = 1.0 to 4.0) and 6.6 grams m -2 (95% CI = 3.6 to 9.6). The relatively larger difference in fresh mass was due to a high proportion of adult individuals above drains. One likely explanation for the pattern of abundance is that the lowered water table level near the drains provides an environment beneficial for the population growth of L. terrestris. Due to the role of L. terrestris burrows as flow paths of percolating water the observations may have implications on subdrain function.

Ontogenetic Scaling of Burrowing Forces in the Earthworm Lumbricus Terrestris

In hydrostatic skeletons, it is the internal fluid under pressure surrounded by a body wall in tension (rather than a rigid lever) that enables the stiffening of the organism, the antagonism of muscles and the transmission of force from the muscles to the environment. This study examined the ontogenetic effects of body size on force production by an organism supported with a hydrostatic skeleton. The earthworm Lumbricus terrestris burrows by forcefully enlarging crevices in the soil. I built a force-measuring apparatus that measured the radial forces as earthworms of different sizes crawled through and enlarged pre-formed soil burrows. I also built an apparatus that measured the radial and axial forces as earthworms of different sizes attempted to elongate a dead-end burrow. Earthworms ranging in body mass m(b) from hatchlings (0.012 g) to adults (8.9 g) exerted maximum forces (F, in N) during active radial expansion of their burrows (F=0.32 m(b)(0.43)) and comparable forces during axial elongation of the burrow (F=0.26 m(b)(0.47)). Both these forces were almost an order of magnitude greater than the radial anchoring forces during normal peristalsis within burrows (F=0.04 m(b)(0.45)). All radial and axial forces scaled as body mass raised to the 2/5 power rather than to the 2/3 power expected by geometric similarity, indicating that large worms exert greater forces than small worms on an absolute scale, but the difference was less than predicted by scaling considerations. When forces were normalized by body weight, hatchlings could push 500 times their own body weight, while large adults could push only 10 times their own body weight.

Long-term reduction of cold hardiness following ingestion of ice-nucleating bacteria in the Colorado potato beetle, Leptinotarsa decemlineata

We investigated the effect of ingestion of ice-nucleating bacteria on the supercooling capacity and cold hardiness of the Colorado potato beetle ( Leptinotarsa decemlineata Say), a freeze-intolerant species that overwinters as adults in shallow, terrestrial burrows. Ingestion of ice-nucleating bacteria ( Enterobacter agglomerans, Pseudomonas fluorescens, Pseudomonas putida, Pseudomonas syringae), fed on slices of potato tuber, caused an abrupt decrease in supercooling capacity. No change occurred in the supercooling capacity of beetles fed Escherichia coli, as this species lacks ice-nucleating activity. Ingestion rates showed that tubers treated with different species were equally palatable. During diapause induction beetles evacuated food from their guts, but nevertheless retained sufficient ice-nucleating bacteria to diminish supercooling. Beetles fed P. fluorescens and P. putida exhibited reduced supercooling even after an 8-wk exposure to simulated winter conditions. Furthermore, P. fluorescens was isolated 10-wk post-ingestion from diapausing beetles. Our data suggest that ingested bacteria may be retained by insects during entry into diapause and that the cold hardiness of candidate crop pests, such as L. decemlineata, may be reduced by feeding them ice-nucleating bacteria prior to winter diapause.

Influence of soil hydric parameters on the winter cold hardiness of a burrowing beetle, Leptinotarsa decemlineata (Say)

This investigation examined the influence of soil moisture and associated parameters on the cold hardiness of the Colorado potato beetle (Leptinotarsa decemlineata Say), a temperate-zone species that overwinters in terrestrial burrows. The body mass and water content of adult beetles kept in sand at 4 °C varied over a 16-week period of diapause according to the substratum's moisture content. Changes in body water content, in turn, influenced the crystallization temperature (range −3.3 to −18.4 °C; n = 417), indicating that environmental moisture indirectly determined supercooling capacity, a measure of physiological cold hardiness. Beetles held in dry sand readily tolerated a 24-h exposure to temperatures ranging from 0° to −5 °C, but those chilled in sand containing as little as 1.7% water (dry mass) had elevated mortality. Thus, burrowing in dry soils not only promotes supercooling via its effect on water balance, but may also inhibit inoculative freezing. Mortality of beetles exposed to −5 °C for 24 h was lower in substrates composed of sand, clay and/or peat (36–52%) than in pure silica sand (78%) having an identical water content (17.0% dry mass). In addition to moisture, the texture, structure, water potential, and other physico-chemical attributes of soil may strongly influence the cold hardiness and overwintering survival of burrowing insects.

Characteristics of macroporosity in a reduced tillage agroecosystem with manipulated earthworm populations: Implications for infiltration and nutrient transport

The effects of macroporosity on the potential for nutrient transport has been extensively studied for no-tillage agroecosystems. The present study was undertaken to quantify macroporosity and to demonstrate the potential for nutrient transport in reduced-tillage systems. Soil macropore area and numbers were quantified by image analysis into three size classes (1–8, 8–16 and > 16 mm 2) at three depths (10, 20 and 30 cm) at two locations (between-row, within-row) in corn agroecosystem enclosures with manipulated earthworm populations (reduction, not manipulated, addition). A dilute solution of latex paint was surface-applied to determine pathways for water infiltration. All macropore sizes contributed to infiltration. Earthworm-treatments had no significant effects on infiltration rates, but rates were significantly faster within crop rows than between rows. In the earthworm-addition plots the area of macropores was significantly greater in the surface soil (10 cm depth) then in the other treatments, indicating re-formation of continuous flow pathways destroyed by tillage practices. The majority of the > 16 mm 2 size pores were recognized as Lumbricus terrestris (L.) burrows, which represented the greatest per cent area of all size classes at the 10 cm depth. The area of these large macropores was significantly greater in addition-treatments than in the other plots at all depths and locations except for 30 cm-deep between-row locations. The absence of an earthworm effect at this location is attributed to the existence of pre-existing burrows that were not disrupted by tillage or root activity and is due to earthworms concentrating their activity in the root-zone, in the within-row location. By increasing soil macroporosity and creating transport pathways of preferential flow, earthworms potentially affect the nutrient transport in leachate and nutrient loss from the agroecosystem.