Eriogonum spergulinum, the Spurry Buckwheat

Wandering around sandy highlands of the southwest United States, you may encounter a sparse, wiry weed growing between five and forty centimetres in height. This is the spurry buckwheat Eriogonum spergulinum.

Spurry buckwheat Eriogonum spergulinum, copyright Dcrjsr.

Members of the buckwheat family Polygonaceae are found worldwide but tend to be easily overlooked as low, scrubby weeds. In North America, one of the most diverse genera is Eriogonum, known from about 250 species though many are difficult to readily distinguish (Hickman 1993). Eriogonum spergulinum is one of the more recognisable species in the genus. As mentioned above, it grows in sandy soils, particularly those dominated by worn-down granite, and is found at altitudes between 1200 and 3500 metres. It is an annual herb with basal leaves of a linear shape, less than two millimetres wide but up to thirty millimetres long. The greater part of the plant's height is made up by the slender, cyme-like inflorescence bearing unribbed, four-toothed involucres on slender stalks. The flowers are up to three millimetres in diameter with a white perianth marked by darker stripes. Overall, E. spergulinum in flower resembles a drifting cloud of small white stars.

Close-up on Eriogonum spergulinum flowers, copyright Tom Hilton.

Three varieties of Eriogonum spergulinum have been recognised though they are not always distinct and tend to intergrade with each other. In most parts of the species' range, plants belong to the variety E. spergulinum var. reddingianum. This variety is characterised by erect inflorescences with glandular axes and flowers about two millimetres in diameter. The other two varieties are both restricted to the Sierra Nevada mountains of California. Eriogonum spergulinum var spergulinum resembles var. reddingianum but produces larger flowers, about three millimetres in diameter. Eriogonum spergulinum var. pratense is more distinctive. Inflorescences are prostrate to ascending, only about two to five millimetres in height, and lack glands on the axes. Flowers are only 1.5 millimetres across. Pratense is also a higher-altitude variety, found at heights above 2500 metres. The Sierra Nevada varieties are both uncommon; if any variety is likely to be found, it is the widespread reddingianum.

REFERENCE

Hickman, J. C. (ed.) 1993. The Jepson Manual: Higher Plants of California. University of California Press: Berkeley (California).

Scaleyness is Next to Diatom-ness

The last few decades have seen significant advances in our understanding of microbial diversity. Consistent improvements in available technologies and methods for study, both molecular and ultrastructural, have allowed researchers to look further and deeper than they ever could before. Not only have they identified taxa that were previously unknown, they have been able to develop a much better understanding of how microbial taxa relate to each other. Among the fields that has seen particularly remarkable advances has been the study of the picoplankton, that component of the marine plankton comprising organisms less than two or three microns in size. Much of the picoplankton, of course, is made up of bacteria but another significant component is species of microalgae belonging to the group known as heterokonts or stramenopiles.

Schematic diagram of motile bolidophyte cell, from Guillou et al. (1999).

Heterokonts are a major clade of eukaryotes that are commonly characterised by cells bearing anterior pairs of morphologically distinct cilia. One of the cilia is longer and bears rows of hairs referred to as mastigonemes; the other, shorter cilium is usually smooth. Many heterokont species are photosynthetic and belong to a subclade of the heterokonts known as the ochrophytes. For most people, the best known ochrophytes will be the often-decidedly-not-microbial brown algae such as kelps. However, ochrophytes also include a broad diversity of microbial forms. Most ochrophyte cells share a characteristic golden-brown coloration owing to the presence of yellowish pigments such as fucoxanthin as well as the more standard chlorophyll.

Recent molecular studies have supported a division of the ochrophytes between two major clades. On one side are the brown algae and their closer microbial relatives. In the other clade are those ochrophytes more closely related to the diatoms. Appropriately enough, this latter clade was dubbed the Diatomista by Derelle et al. (2016). Other than the diatoms themselves, most representatives of the Diatomista belong to the picoplankton. For the most part, diatoms have lost the cilia otherwise associated with heterokonts. The only exceptions are the reproductive sperm cells which have a single anterior cilium bearing mastigonemes (Adl et al. 2019). The remaining Diatomista commonly have cells bearing one or two anterior cilia (if only one cilium is present, it will typically have mastigonemes). Nevertheless, the basal apparatus of the cilia is reduced, lacking microtubular roots or a rhizoplast, suggestive of an intermediate stage towards total loss (Guillou et al. 1999). Many also bear a covering of silica scales; enlargement of individual scales may have lead to the evolution of diatom-style frustules.

Non-motile cell of Triparma laevis f. inornata, from Kuwata et al. (1987).

The closest known relatives of diatoms are currently classified as the class Bolidophyceae. Motile cells of the Bolidophyceae were first described in 1999 (Guillou et al. 1999). They possessed two cilia, with the haired cilium directed anteriorly and the smooth cilium directed posteriorly, and lacked silica scales. Nevertheless, they were identified as the sister group to diatoms by molecular data. This was corroborated by the absence of a transitional helix structure at the base of each cilium, a feature shared with diatom sperm cells. Guillou et al. (1999) commented on the relatively high mobility of the bolidophytes, in contrast to the general expectation that picoplankton should exhibit a reduction in individual cell mobility owing to the difficulty in meeting energy demands.

The concept of bolidophytes shifted somewhat in the 2010s with the isolation in culture of the Parmales, a group of minute eukaryotes that had first been recognised in the 1980s but had long eluded detailed characterisation. These were non-motile cells enclosed within ornate silica scales. Once molecular data become available, researchers realised that 'Parmales' were not just closely related to 'bolidophytes', they were close enough that the two forms could reasonably be included in a single genus (Kuwata et al. 2018). The exact details of their connection, however, remain uncertain. It seems likely that the flagellate and non-flagellate forms represent alternate forms of single species. But whether we are looking at alternate generations of the life cycle, or whether the flagellate cells are generated in response to particular conditions, remains to be determined.

Skeleton of silicoflagellate Dictyocha speculum, copyright Proyecto Agua.

The remaining members of the Diatomista form a clade currently treated as including three classes, the Dictyochophyceae, Pelagophyceae and Pinguiophyceae. Together they are a diverse array of minute organisms, whether ciliated or amoeboid, naked or carrying organic scales, photosynthetic or heterotrophic or some combination of both. Among the representatives of the Dictyochophyceae are the so-called silicoflagellates, ciliated cells reinforced with a skeleton of (duh) silica. Though only a few species of silicoflagellate are recognised in the modern environment, they have an extensive fossil record extending back to the Middle Cretaceous (Kristiansen 1990). In some places, their preserved skeletons may dominate rock formations. Silicoflagellates appear to have reached their peak in the Miocene, followed by a decline to their modern condition. The exact interpretation of the silicoflagellate fossil record is a long-standing challenge (whether differences in morphology are taxonomic or environmental, for instance) but they hold the potential to tell us much about the history of our seas.

REFERENCES

Adl, S. M., D. Bass, C. E. Lane, J. Lukeš, C. L. Schoch, A. Smirnov, S. Agatha, C. Berney, M. W. Brown, F. Burki, P. Cárdenas, I. Čepička, L. Chistyakova, J. del Campo, M. Dunthorn, B. Edvardsen, Y. Eglit, L. Guillou, V. Hampl, A. A. Heiss, M. Hoppenrath, T. Y. James, A. Karnkowska, S. Karpov, E. Kim, M. Kolisko, A. Kudryavtsev, D. J. G. Lahr, E. Lara, L. Le Gall, D. H. Lynn, D. G. Mann, R. Massana, E. A. D. Mitchell, C. Morrow, J. S. Park, J. W. Pawlowski, M. J. Powell, D. J. Richter, S. Rueckert, L. Shadwick, S. Shimano, F. W. Spiegel, G. Torruella, N. Youssef, V. Zlatogursky & Q. Zhang. 2019. Revisions to the classification, nomenclature, and diversity of eukaryotes. Journal of Eukaryotic Microbiology 66: 4–119.

Derelle, R., P. López-García, H. Timpano & D. Moreira. 2016. A phylogenomic framework to study the diversity and evolution of stramenopiles (=heterokonts). Molecular Biology and Evolution 33 (11): 2890–2898.

Guillou, L., M.-J. Chrétiennot-Dinet, L. K. Medlin, H. Claustre, S. Loiseaux-de Goër & D. Vaulot. 1999. Bolidomonas: a new genus with two species belonging to a new algal class, the Bolidophyceae (Heterokonta). Journal of Phycology 35: 368–381.

Kristiansen, J. 1990. Phylum Chrysophyta. In: Margulis, L., J. O. Corliss, M. Melkonian & D. J. Chapman (eds) Handbook of Protoctista. The structure, cultivation, habitats and life histories of the eukaryotic microorganisms and their descendants exclusive of animals, plants and fungi. A guide to the algae, ciliates, foraminifera, sporozoa, water molds, slime molds and the other protoctists pp. 438–453. Jones & Bartlett Publishers: Boston. Kuwata, A., K. Yamada, M. Ichinomiya, S. Yoshikawa, M. Tragin, D. Vaulot & A. Lopes de Santos. 2018. Bolidophyceae, a sister picoplanktonic group of diatoms—a review. Frontiers in Marine Science 5: 370.

Glyphyalinia Snails

North America (as with pretty much everywhere in the world outside the coldest regions) is home to a wide diversity of small, terrestrial snails that tend to pass unnoticed. Among the more diverse of these is the zonitid genus Glyphyalinia.

Glyphyalinia carolinensis, copyright John Slapcinsky.

Glyphyalinia species are often found in forest leaf-litter in the eastern part of North America. They have a low, translucent shell that is often about half a centimetre in diameter. Whorls of the shell increase regularly in size and are marked by a series of strongly impressed radiating lines in addition to finer growth lines. The umbilicus of the shell varies between species from completely absent to quite wide (Burch & Pearce 1990). The soft body of the animal varies in coloration, again depending on species. That of G. roemeri is all white except for the eyes; that of G. wheatleyi is almost uniformly black. The reproductive system of Glyphyalinia (which are hermaphroditic) includes a well-developed epiphallus and a distinct, ovoid spermathecal sac (Baker 1930).

Multiple species of Glyphyalinia may be found living in a single patch of forest though, at present, we know little about how (and whether) micro-habitats are partitioned between species. Some species seem to tolerate a wide variety of soil types and are correspondingly widely distributed. Others are more selective and localised; some may be considered endangered by habitat degradation. Even supposedly widespread species may be more vulnerable than appreciated: at least some may represent clusters of closely related species rather than truly uniform populations. These tiny snails can be notoriously difficult to study, making for a risk that they might just slip away barely noticed.

REFERENCES

Baker, H. B. 1930. The North American Retinellae. Proceedings of the Academy of Natural Sciences of Philadelphia 82: 193–219.

Burch, J. B., & T. A. Pearce. 1990. Terrestrial Gastropoda. In: Dindal, D. L. (ed.) Soil Biology Guide pp. 201–309. John Wiley & Sones: New York.

Williamsita

A while back, I wrote a post about the crabronid wasp genus Podagritus. This time, I'm going to cover another crabronid genus found here in Australia: Williamsita.

Williamsita sp., copyright David Francis.

Like Podagritus, Williamsita species are boldly coloured wasps, typically mostly black with contrasting yellow or orange markings. They differ from Podagritus species in being more robust with the base of the gaster not notably pedunculate. Other distinguishing features include the presence of distinct foveae (pits) against the margins of the eyes (occasionally less distinct in males), thirteen-segmented antennae in males, and a pygidial plate in both sexes that is narrowed and concave in females, quadrate in males. Williamsita species also do not have the palps reduced as in Podagritus, instead having the more typical arrangement of six segments in the maxillary palps and four segments in the labial palps (Bohart & Menke 1976).

To date, eleven species have been recognised in the genus Williamsita (Leclercq 2006). Most are found in Australia with a single species each known from New Caledonia and Vanuatu. Leclercq (1950) suggested dividing the genus between two subgenera with all species except the New Caledonian type species W. novocaledonica forming a subgenus Androcrabro. Features supporting the latter taxon included the presence of ventral notches on one or more segments of the antennae in males. However, Leclercq later suggested abandoning such a formal division, questioning its significance (Leclercq 2006). The Australian species of Williamsita are, nevertheless, distinct from the two insular species in being marked with much stronger punctation over the body.

Most Williamsita species remain little seen and poorly known. However, breeding habits have been recorded for two Australian species, W. bivittata and W. tasmanica (Maynard & Fearn 2021; McCorquodale et al. 1989). Both these species nest in branching holes in rotting wood, either commandeering burrows left by wood-boring insects or excavating their own. Prey consists of larger flies such as blow flies or soldier flies which were carried back to the nest by the wasp running with the fly carried below the body. Up to six paralysed flies might be placed lying on their backs in a nest cell with an egg laid across the 'throat' (i.e. at the joint between head and thorax) of one of the flies. The cell would then be closed with a plug of woody frass. McCorquodale et al. (1989) recorded W. bivittata constructing several such cells in a series along a single tunnel, whereas Maynard & Fearn (2021) found W. tasmanica more likely to place a single cell in a side-branch. As both observations were limited to a single location in a single season, though, one might reasonably question whether these represent true differences in species behaviour or were determined by available conditions. There's a limit to how deep a Williamsita can burrow.

REFERENCES

Bohart, R. M., & A. S. Menke. 1976. Sphecid Wasps of the World. University of California Press: Berkeley.

Leclercq, J. 1950. Sur les crabroniens orientaux et australiens rangés par R. E. Turner (1912–1915) dans le genre Crabro (subgenus Solenius). Bulletin et Annales de la Société Entomologique de Belgique 86 (7–8): 191–198.

Leclercq, J. 2006. Hyménoptères crabroniens d'Australie du genre Williamsita Pate, 1947 (Hymenoptera: Crabronidae). Notes Fauniques de Gembloux 59 (2): 115–119.

Maynard, D., & S. Fearn. 2021. Ecological and behavioural observations of a nesting aggregation of the endemic Tasmanian digger wasp Williamsita tasmanica (Smith, 1856) (Hymenoptera: Crabronidae: Crabroninae). Papers and Proceedings of the Royal Society of Tasmania 155 (1): 43–50.

McCorquodale, D. B., C. E. Thomson & V. Elder. 1989. Nest and prey of Williamsita bivittata (Turner) (Hymenoptera: Sphecidae: Crabroninae). Australian Entomological Magazine 16 (1): 5–8.

Opening Dors

My current dayjob mostly revolves around identifying and counting dung beetles. When Europeans settled Australia, they brought their farm animals with them. Unfortunately, the large piles of dung produced by cattle and horses proved rather daunting to native scavengers used to the more compact droppings of kangaroos and possums. And if you've ever experienced an Australian summer, you'll know that flies are definitely a thing. To help with this situation, Australia has had a long-running programme introducing exotic dung beetles that are better able to clean up after livestock. Most of these are members of the typical dung beetle family Scarabaeidae but one species, Geotrupes spiniger, represents a different subgroup of the superfamily Scarabaeoidea. These are the earth-boring dung beetles or dor beetles of the Geotrupidae.

Dor beetle Geotrupes spiniger, copyright Udo Schmidt.
The geotrupids are medium-sized to very large beetles, ranging in size from half a centimetre to 4.5 cm in length (Jameson 2002). Like many other members of the Scarabaeoidea, they have broad fore legs used for digging. Their short, eleven-segmented antennae end in the asymmetrical club typical of scarabaeoids but they may be distinguished from other families in that the basal segment of the three-segmented club is expanded to form a 'cup' against which the other segments may be tightly closed. The body of geotrupids is strongly convex, and is smooth and shiny dorsally but hairy underneath. In many species, the males may bear elaborate horns and/or processes on the head and pronotum.

Male Taurocerastes patagonicus, copyright Nicolás Lavandero.

Despite their size, geotrupids are secretive animals, spending most of their time in burrows underground (which may be up to three metres in depth) and usually only emerging at night. Various species feed on animal dung or decaying matter; some feed on subterranean fungi. In at least some species, eggs are laid in brood chambers within the parent's home burrow and multiple life stages may share a single burrow. Burrows may also be shared between multiple adults when conditions demand. Though adults do not directly tend to larvae, they may stock brood chambers with food supplies. In some Australian species of the subfamily Bolboceratinae, females lay a single gigantic egg at a time that may be up to 56% the size of its layer (Houston 2011). Larvae hatching from such an egg are able to develop right through to maturity without feeding.

Adult geotrupids produce a stridulating noise when disturbed which is the origin of the alternate vernacular name of "dor beetle" ("dor" being an old word for a buzzing insect). Larvae may or may not be capable of stridulation, depending on the species.

Male Blackburnium rhinoceros, copyright Edward Bell.

The classification of geotrupids is the subject of ongoing investigation. A recent classification divides the family between three subfamilies, the widespread Geotrupinae and Bolboceratinae and the South American Taurocerastinae. Morphological differences between these subfamilies, particularly at the larval stage, have lead some researchers to question whether the Geotrupidae in the broad sense represents a monophyletic group. Molecular analyses thus far seem ambiguous; an analysis by McKenna et al. (2015) placed geotrupids as part of a polytomy near the base of the scarabaeoids. As an aside, my supervisor recently asked myself and a retired colleague whether Geotrupes spiniger was the only species of geotrupid found in Australia. I replied "yes", our colleague responded "no". Our conflict, of course, was based on whether Australia's wide diversity of Bolboceratinae contributed to the count.

REFERENCES

Houston, T. F. 2011. Egg gigantism in some Australian earth-borer beetles (Coleoptera: Geotrupidae: Bolboceratinae) and its apparent association with reduction or elimination of larval feeding. Australian Journal of Entomology 50: 164–173.

Jameson, M. L. 2002. Geotrupidae Latreille 1802. In: Arnett, R. H., Jr, M. C. Thomas, P. E. Skelley & J. H. Frank (eds) American Beetles vol. 2. Polyphaga: Scarabaeoidea through Curculionoidea pp. 23–27. CRC Press.

McKenna, D. D., B. D. Farrell, M. S. Caterino, C. W. Farnum, D. C. Hawks, D. R. Maddison, A. E. Seago, A. E. Z. Short, A. F. Newton & M. K. Thayer. 2015. Phylogeny and evolution of Staphyliniformia and Scarabaeiformia: forest litter as a stepping stone for diversification of nonphytophagous beetles. Systematic Entomology 40: 35–60.

Platybunus: the Wide-Eyed Harvestmen of Europe

The western Palaearctic region (that is, Europe and the immediately adjacent parts of Asia and northern Africa) is home to a diverse and distinctive fauna of harvestmen. Among the various genera unique to this part of the world are the forest- and mountain-dwellers of the genus Platybunus.

Platybunus pinetorum, copyright Donald Hobern.

Platybunus species are moderate-sized long-legged harvestmen of the family Phalangiidae, the central body in larger individuals being about eight millimetres long (Martens 1978). Their most characteristic feature is a relatively large eye-mound, distinctly wider than long and occupying a large section of the anterior carapace. As with other European phalangiids, they eye-mound is ornamented with a row of denticles each side though the body lacks denticles over the remainder of the dorsum. The body is often comparatively slender, tapering towards the rear (particularly in males), and is marked on the dorsum by a darker median band. The pedipalps have a pair of well-developed setose apophyses on the inner distal ends of the patella and tibia, and a series of long spine-like tubercles on the underside of the femur. These tubercles presumably function in the capture of prey, forming a basket that can be closed around the harvestman's victims. External sexual dimorphism in Platybunus is fairly minimal though females are overall larger and fatter. The penis is notably long and slender with a relatively small glans, offset from the shaft by a more or less marked constriction.

Platybunus bucephalus, copyright Adrian Tync.

Martens (1978) recognises four species of Platybunus found in higher altitude regions of central Europe with the species P. bucephalus and P. pinetorum occupying much of the genus' range. Platybunus bucephalus may be distinguished from P. pinetorum by, among other features, its relatively shorter legs. Platybunus pallidus is endemic to the Carpathians, and the tiny P. alpinorelictus inhabits the Garda Mountains of northern Italy. Another species, P. anatolicus, was described from Turkey by Roewer (1956)*. In general, Platybunus species inhabit alpine and subalpine forests, being found among the herbaceous undergrowth, under bark or on rock faces. Where their ranges overlap, P. bucephalus is more accustomed to extending beyond the forest margins than P. pinetorum and may be found above the tree-line. In recent years, the range of P. pinetorum has extended northwards, being first recorded from the UK in 2010 and Sweden in 2015 (Fritzén et al. 2015). At least some populations of P. pinetorum are capable of reproducing parthenogenetically and this may have played a part in its spread.

*Platybunus mirus was described by Loman (1892) on the basis of two male specimens that supposedly came from Sumatra. Though the identity of this species has never been resolved (Loman's illustration of the penis is at least suggestive of a true Platybunus), the claimed locality seems almost certain to be an error of some kind.

The internal classification of the Phalangiidae remains in need of further investigation. Platybunus has been recognised by some authors as forming a subfamily Platybuninae with a cluster of other western Palaearctic genera bearing similar ventrally spined pedipalps (Zhang & Zhang 2012). However, other authors have not separated this group from the subfamily Phalangiinae. The platybunines may represent a phylogenetically coherent grouping, or their shared features may reflect adaptations to a similar life style. The genital morphology of Platybunus is recognisably distinct from that of other platybunines which may argue against any relationship (Martens 1978). On the other hand, platybunines might possibly be distinguished from phalangiines by the chemical composition of their repugnatorial gland secretions (Raspotnig et al. 2015). A formal analysis of the family's evolution would be a welcome advance.

REFERENCES

Fritzén, N. R., V. Rinne, M. Sunhede, A. Uddström, S. Van de Poel & P. De Smedt. 2015. Platybunus pinetorum (Arachnida, Opiliones) new to Sweden. Memoranda Soc. Fauna Flora Fennica 91: 37–40.

Loman, J. C. C. 1892. Opilioniden von Sumatra, Java und Flores. In: M. Weber (ed.) Zoologische Ergebnisse einer Reise in Niederländisch Ost-Indien vol. 3 pp. 1–26, pl. 1. E. J. Brill: Leiden.

Martens, J. 1978. Spinnentiere, Arachnida: Weberknechte, Opiliones. Gustav Fischer Verlag: Jena.

Raspotnig, G., M. Schaider, P. Föttinger, V. Leutgeb & C. Komposch. 2015. Benzoquinones from scent glands of phalangiid harvestmen (Arachnida, Opiliones, Eupnoi): a lesson from Rilaena triangularis. Chemoecology 25: 63–72.

Roewer, C. F. 1956. Über Phalangiinae (Phalangiidae, Opiliones Palpatores). (Weitere Weberknechte XIX). Senckenbergiana Biologica 37 (3–4): 247–318.

Zhang, C., & F. Zhang. 2012. On the subfamilial assignment of Platybunoides (Opiliones: Eupnoi: Phalangiidae), with the description of a new species from China. Zootaxa 3190: 47–55.

Voley, Voley, Voley

Over a third of all living mammal species are rodents. In cooler regions of the Northern Hemisphere, the rodent fauna is often dominated by the Microtinae, the group of mouse-like rodents including voles and lemmings. And in North America, the most widespread of all microtine species is the eastern meadow vole Microtus pennsylvanicus.

Eastern meadow vole Microtus pennsylvanicus, copyright Gilles Gonthier.

The eastern meadow vole is found over most of Canada and a large part of the northern and eastern United States, with the subspecies M. p. chihuahuensis known from Chihuahua in northern Mexico. This species is about the size of a small rat, being from 14 to 20 cm in length with about three to six centimentres of that length being tail (Reich 1981). They are generally yellowish-brown in colour with black tips on the hairs though individuals vary significantly in brightness and shade. Western populations are supposed to be lighter in coloration than eastern, and southern individuals tend to be larger than northern. As an indication of this species' variability, Reich (1981) recognised 28 recognised subspecies.

Eastern meadow voles are primarily inhabitants of grasslands, with a preference for damper habitats, though they may also be found in woodlands. They mostly live in burrows underground, emerging to the surface to forage for food. Eastern meadow voles are generalist feeders, browsing on most available forms of low vegetation: grasses, sedges and herbs. When populations reach their peak, they may cause significant damage to woody plants by ringbarking their trunks. Individuals may seemingly be active at just about any time of day.

Eastern meadow vole in a state of danger, copyright David Allen.

Like other small rodents, meadow voles are short-lived animals with estimates of average lifespan ranging from just two or three months to ten to fourteen months (Reich 1981). Studies of movement patterns indicate that mature females generally maintain distinct, non-overlapping ranges whereas males range further and with less concern for others (Madison 1980). Mating behaviour appears generally promiscuous: males will range over the territories of multiple females and litters with mixed paternity are not uncommon (Boonstra et al. 1993). Paternal behaviour has been observed among eastern meadow voles in laboratory populations but all indications are that wild males do not remain with females after mating. Males often bear wounds indicative of intra-species conflict. These may be the result of males fighting over access to females but Madison (1980) suggested a potential alternative. Less dominant males might be more likely to attempt to approach females earlier or later in their oestrus cycle as the females are more likely to be guarded by dominant males when at their peak. While avoiding attacks from their dominant brethren, these minor males might find themselves violently rebuffed by a female who is just not yet in the mood.

After mating, gestation lasts for about three weeks, usually resulting in a litter of four to six babies. Weaning then takes place after about two weeks. Females forage far less while lactating than at other times. It might seem counter-intuitive for a female to reduce feeding when her energy demands are presumably at their peak but again Madison (1980) suggests an explanation: perhaps her energy needs are such that she simply lacks the capacity for extensive wandering. Young may potentially remain with their mother for some time after weaning but eventually they will be forced out of the parental burrow, leaving to face the wide world on their own. And when you're the size of a vole, that's a very wide world indeed.

REFERENCES

Boonstra, R., X. Xia & L. Pavone. 1993. Mating system of the meadow vole, Microtus pennsylvanicus. Behavioral Ecology 4: 83–89.

Madison, D. M. 1980. Space use and social structure in meadow voles, Microtus pennsylvanicus. Behavioral Ecology and Sociobiology 7: 65–71.

Reich, L. M. 1981. Microtus pennsylvanicus. Mammalian Species 159: 1–8.