Invertebrata    items from issue no. 20 

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Pycnogonids (sea spiders) of southeastern Australia and Tasmania
Invertebrata 20, July 2001

The coastlines of southeastern Australia and Tasmania are virtually unexplored in terms of some of the smaller invertebrate groups, particularly the sea spiders or Pycnogonida. The most up-to-date list of pycnogonid species for all of Australia can be found at www.invertebrate.ws, which is my personal website (cf www.personal.monash.edu.au/~fgodevic//seaspider/index.htm). This list has 81 species of pycnogonids and is far from complete. For the last three years, I have been doing some sporadic pycnogonid collecting from areas such as Westernport Bay, Port Philip Bay and Kennett River (near Apollo Bay) here in Victoria, and nearly every pycnogonid I have found so far is a new species. My most recent collection, from South Channel Fort in Port Philip Bay, also contains at least one new genus. I spend most of my collecting time carefully looking through clumps of red algae, bryozoans, mussels, etc. and it really helps to take most of this stuff back to the lab and sort through it under a dissecting microscope as most of the new species (and the new genus) tend to be very small (1-2 mm) and nondescript (white or yellowish in colour), which may explain why they have been overlooked in the past.

Nearly all of the larger and more colourful pycnogonids from this area have already been described since they are easily spotted and make nice colourful photographs for dive brochures and magazine covers. In fact, over the past two years, many of the larger and more colourful species from here have found their way into a number of different publications including National Geographic (October 1999), Australian Geographic (January-March 2000), Fisheries, New South Wales (Summer 2000), and Newton (a new Australian Geographic Society publication) (May-June 2001). It is interesting that even though all of these species have been described before and most could have been easily identified by reading the key in Staples (1997), nearly all of them were published as a 'pycnogonid' or 'sea spider.' The National Geographic at least had its photo identified to genus (Pseudopallene) and only Newton had their picture identified down to species (Colossendeis colossea).

Another area of pycnogonid biology I am currently working on is pycnogonid larval development. I have just completed a review article and a paper describing development in an Antarctic pycnogonid, Austropallene cornigera, and hope to have them both published soon. Most books and articles on pycnogonids will tell you that there is only one kind of pycnogonid larva, the protonymphon, and after that, they tend to be very vague on the details of pycnogonid development. It turns out, if one looks into the question in more detail, that there are at least four different ways in which a pycnogonid can go from egg to adult (Typical Protonymphon, Encysted Larva, Atypical Protonymphon, Attaching Larva), and a protonymphon larva, depending on species, can develop along any one of the first three pathways described above.

The Typical Protonymphon, characteristic of most ammotheids, is a free-living larva which gradually, through a series of molts, becomes an adult. The Encysted Larva, confined to the Family Phoxichilidiidae and to one North American ammotheid, hatches from the egg and goes directly to a bed of hydroids or corals where it then becomes encysted in the polyp or gastrozooid (see Staples (1997) for some nice colour photos of these larvae). It remains there for several molts and usually re-emerges from the hydroid as a young juvenile with three pairs of walking legs. The Atypical Protonymphon also uses a marine invertebrate for a temporary host and this larval type has been found living on a polychaete, Sabella melanostigma, in the Gulf of California and also inside several different Japanese clams (Ruditapes philippinarum, Hiatella orientalis). We don't know much else about development in the Atypical Protonymphon except that the adults in all cases are free-living and the larvae and juveniles are confined to their temporary hosts. The fourth type of pycnogonid development, the Attaching Larva, is found only in the families Nymphonidae and Callipallenidae. This larva looks more like an embryo than anything else (see Nakamura (1981) for pictures) and as soon as it hatches, it glues itself to the parent's ovigerous legs and stays there for the next several molts. It usually leaves the parent and takes up a free-living existence once it becomes a young juvenile with (depending on species) either two or three pairs of walking legs.

I am starting work soon on a monograph of new pycnogonid genera and species from southeastern Australia (including Tasmania) and I would be very interested in examining any pycnogonid specimens which have been collected from this area. You can send specimens to me at Monash University (address below). Either live or preserved specimens are fine since we have facilities to keep live ones and whenever possible, I try to keep them alive for a few months so that I can photograph them and take notes on feeding behaviour, larvae, etc. Live pycnogonids do well in the post if they are placed in a small vial of sea water and are shipped by express mail. Most species will survive for several days like this and in one case (probably an exception!), I had live specimens shipped to me from Queensland which had spent a week in transit and survived just fine. When in doubt, preserve them first in 70% alcohol.

Bonnie A. Bain
School of Biological Sciences
Monash University
Clayton VIC 3800
bonnie.bain@sci.monash.edu.au

Further information:

Arnaud, F. and Bamber, R.N. 1987. The Biology of the Pycnogonida, pp. 1-96 in Blaxter, J.H.S. and Southward, A.J. (eds), Advances in Marine Biology, vol. 24. New York: Academic Press.

Clark, W. C. 1963. Australian Pycnogonida. Records of the Australian Museum 26(1): 1-81.

Edgar, G. J. 2000. Australian Marine Life (revised edition). Sydney: Reed New Holland. (Pycnogonids on pp. 166-167).

Nakamura, K. 1981. Post-embryonic development of a pycnogonid, Propallene longiceps. Journal of Natural History 15: 49-62.

Staples, D. A. 1997. 21. Sea spiders or pycnogonids (Phylum Arthropoda), pp 1040-1072 in Shepherd, S.A. and Davies, M. (eds.), Marine Invertebrates of Southern Australia, Part III. Adelaide: South Australian Research and Development Institute.

pycnogonids


Ventral views of two pycnogonid (sea spider) larvae.
Left: Protonymphon. Right: Attaching larva.



Forestry Tasmania and IBOY invertebrate projects
Invertebrata 20, July 2001

IBOY is the International Biodiversity Observation Year (actually it lasts for three years!). IBOY is an attempt to link international programs of research and provide baseline data to monitor future environmental changes within ecosystems. Forestry Tasmania has several projects linked to IBOY utilising the Warra Long Term Ecological Research site in southern Tasmania. Warra is a core site in Forest Ecosystems, a subset of IBOY projects. The IBOY projects are:

DIWPA-IBOY: Canopy Fogging

A contract with the Museum of Victoria, to provide equipment and expertise, has been finalised for a weeklong canopy fogging exercise at Warra. Several tree canopies within the major forest types will be fogged with a synthetic pyrethroid insecticide and the specimens collected in suspended canopy collectors. This exercise will provide a snapshot of the Spring invertebrate fauna inhabiting the upper foliage. Canopy fogging of rainforest (wet forest) trees will be conducted at 18 sites on a latitudinal transect from Japan to Tasmania during spring 2001.

GLIDE-IBOY: Litter decomposition

An international project conducted in 20 countries using identical protocols. The project will examine the impact of invertebrates on rates of litter decomposition using standard litterbags prepared by Colorado State University. The project will run for one year commencing July 2001.

MACROFAUNA-IBOY: Soil invertebrate communities

A project involving 21 countries examining soil invertebrate communities which impact on soil fertility. Management of these communities is now considered an efficient way to improve the sustainability of land utilisation. A standard protocol for invertebrate extraction from soil samples has been defined and the prepared specimens will be sent to France for processing. Sites will be sampled four times during the next twelve months.

ALTITUDINAL TRANSECT-IBOY: Altitudinal biodiversity

This project has been proposed to IBOY as a Tasmanian initiative. The Mt Weld/Warra altitudinal transects are being monitored by FT and DPIWE in a joint project to determine baseline invertebrate data for future environmental change surveys. Sampling using pitfall traps and malaise traps has commenced at each 100-metre altitude increment from 100 to 1300 m.

A poster display on this initiative will be presented at the Australian Entomological Society conference in Sydney. For more on IBOY, see www.nrel.colostate.edu/IBOY.

Dick Bashford
Warra Invertebrate Project Coordinator
Forestry Tasmania
GPO Box 207B
Hobart TAS 7001
Dick.Bashford@forestrytas.com.au



Tasmanian earthworm grows second head
Invertebrata 20, July 2001

During my Tasmanian earthworm studies, I came across a native specimen that was an anterior regenerate - it was growing a replacement 'head' (Fig. 1). This phenomenon is well reported in exotic species, but this is the first confirmation for an Australian native. I have frequently observed both tail and head regenerates of Perionyx excavatus Perrier, 1872; have once seen Pontoscolex corethrurus (Muller, 1856) in the process of growing a new head; and have collected a specimen of Lumbricus rubellus Hoffmeister, 1843 with this condition (specimen ANIC:RB.01.01.01). The present report and sketch will help convince skeptics who, while accepting posterior regeneration, doubt that it is possible for worms to grow new heads. Such regrowth is often in response to mechanical damage from predators or the garden spade, but it may also be evoked by disease and tail autotomy (Stephenson 1930). G.E. Gates spent 10 years studying regeneration in a variety of species, but 'because little interest was shown' he only published a few of his findings that, nevertheless, show it is theoretically possible to get two whole worms from a bisected specimen of certain species. His reports (see Gates 1972) included:

Eisenia fetida (Savigny, 1826) with head regeneration, in an anterior direction, possible at each intersegmental level back to and including 23/24, while tails may be regenerated at any levels behind 20/21.

Lumbricus terrestris Linneus, 1758 can replace anterior segments from as far back as 13/14 and 16/17 but tail regeneration has never been found for this species.

Perionyx excavatus Perrier, 1872 readily regenerates lost parts of the body, in an anterior direction from as far back as 17/18 and a new tail is possible from as far forward as 20/21.

The specimen shown here shows typical characteristics of regeneration: the regrown segments are thinner and paler than normal; one segment (6?) has also been deleted. Queen Victoria Museum (QVM) collection notes for this specimen record the site as Tombstone Creek Forest Reserve (41°23'S, 147°42'E), north-east Tasmania. The actual species is not characterized as no dissection was attempted, however it is possibly one of the 230 species now known from Tasmania (see Blakemore 2000), and is superficially close to Perionychella richea (Spencer, 1895).

Rob Blakemore
robblakemore@bigpond.com

Further information:

Blakemore, R.J. 2000. Tasmanian Earthworms. CD-ROM monograph with review of world families. Pp. 800 including 222 figures. Published by VermEcology, PO BOX 414, Kippax ACT 2615. ISBN 0-646-41088-1.

Gates, G.E. 1972. Burmese Earthworms, an introduction to the systematics and biology of Megadrile oligochaetes with special reference to south-east Asia. Transactions of the American Philosophical Society 62(7): 1-326.

Stephenson, J. 1930. The Oligochaeta. Oxford: Oxford University Press.

earthworm



Parental care in leeches
Invertebrata 20, July 2001

A goal of evolutionary biology is to explain why species evolve different behaviours in response to factors that challenge their survival and reproduction. The evolution of parental care in animals is especially difficult to explain due to the variety of methods by which species have overcome the problems associated with caring for young in diverse environments. The study of parental care examines, in detail, the various methods by which different animal groups successfully care for their developing eggs and young. Diversity in parental care strategies ranges from the abandonment of eggs either by broadcast spawning or by depositing eggs on a suitable substrate, to nesting with extensive care of the eggs and hatchlings, and finally to bearing live young (vivipary) and then rearing them until they are able to care for themselves.

Most research into the evolution of parental care has focused on vertebrate species with few studies examining non-social insects or other invertebrate groups (Clutton-Brock 1991). In an attempt to expand our knowledge and to gain a better understanding of the evolution of parental care in general we have started a research effort to investigate the evolution of parental care in a currently under-studied invertebrate group, the glossiphoniid leeches. Glossiphoniids can be found in lakes, ponds and the slower portions of streams and rivers in Tasmania and throughout the mainland of Australia. There are currently ten species recognised from Australia (two of which are restricted to Tasmania). It is likely, however, that there are still many undescribed Australian species.

Although 'leech' is often considered synonymous with selfishness and exploitation, many leeches are devoted parents. After fertilisation, sexually mature leeches produce cocoons that contain a variable number of eggs (depending on species). In many non-glossiphoniid leeches, the cocoon contains stored energy that sustains the developing eggs and hatchlings with no further investment from the parents. However, in the Glossiphoniidae, parental care ranges from abandonment after egg deposition, to parental brooding of egg clusters in a external nest, to the brooding of eggs and young on the parent's body, to internal gestation in a marsupial-like pouch. In addition, some genera (e.g. Glossiphonia) are known to transfer nutrients across the body wall to the developing young in a manner reminiscent of a 'placenta' (Sawyer 1986; Kutschera & Wirtz 1986a, 1986b; Kutschera 1989, 1992; De Eguileor et al. 1994; Davies et al. 1997; Govedich & Davies 1998). Unlike non-glossiphoniids, the energy required for development and growth in glossiphoniids comes from both the egg yolk and the parent.

During 2001 two honours students from Monash University have begun looking at costs and benefits of parental care in Helobdella papillornata. To this end Lauryne Grant will be examining the influence of varying the duration of care on the individual fitness of both parents and juveniles. George D. Cunningham is working on clutch size.

Duration of care

In wild populations, time between fertilisation of eggs and their attachment to the ventral surface is approximately one week. The eggs are then brooded on the ventral surface of the leech in a fluid filled membranous sac for approximately one week. After hatching, juveniles are brooded on the adult for approximately three weeks (Govedich & Davies 1998). During this time it is thought the adults provide care to the young through several mechanisms, including direct feeding where the parent captures prey and passes the food directly to the young (Davies et al. 1997). The degree to which the young depend on the food provided by their parent has not been extensively studied particularly for juveniles in the later stages of development. In addition, direct nutrient transfer across the body wall from the parent to the developing young has been found in the genus Glossiphnonia (de Eguileor et al. 1994). How common this type of nutrient transfer occurs is not known, and H. papillornata has not been studied to determine if nutrients are transferred. Parents also act in a protective role, defending their young against predators. Additionally, the composition and importance of the fluid in the membranous sac surrounding the eggs is unknown.

L.J. Grant's initial experiment will involve manipulation of the degree of care juveniles receive. This will be achieved by detaching juveniles from their parent at different stages of development. The effect of these varied levels of care will be examined for both the adult and the juvenile. Growth rate and reproductive timing are the major factors used to estimate the fitness of adults and juveniles. Parental care mechanisms including parental feeding, protection and membranous sac contents will be examined. This study will include artificial feeding experiments, to determine whether survival of detached juveniles is enhanced when food is artificially provided. Response to predators will be investigated in order to discover whether brooding adults respond differently to non-brooding adults in the presence of predators. Predator size and type may also be varied to determine whether brooding adults have different responses to predators that threaten their young. Additionally, fluid within the membranous sac surrounding the eggs will be tested in order to determine its composition.

Clutch size

Two types of conflict influencing the size of clutches will be studied, sibling conflict and parent-sibling conflict. These conflicts will occur due to the different interests of the parent and its offspring in 'attempting' to maximise their own (inclusive) reproductive fitness.

Sibling conflict can occur when an individual raises its individual fitness to an extent that compensates for a lowering of its siblings' fitness. This can lead to fatal sibling competition, termed siblicide, or 'cainism'. Thus some individuals in the brood will be selected to eliminate siblings either through direct means (killing of siblings) or through competition (control of resources). The degree and severity of this competition is likely to increase as resources are reduced, and as clutch size is increased (Mock & Parker 1997). Parent-sibling conflict arises when the parent attempts to maximise the fitness of the current and future broods in conflict with the interests of individuals in the current brood (Mock & Parker 1997).

G. D. Cunningham will examine sibling competition and parent-sibling conflict by altering the clutch sizes of Helobdella papillornata. The relationship between these conflicts and the number of juveniles in a given clutch will be estimated by examining the health of juveniles, and parents. Juveniles will be removed or added to a brood and a digital camera will be used to record the growth rate, size and survivorship of individuals to estimate the fitness of juveniles. Parental fitness will be estimated using growth rate, and time to and size of the next clutch.

Why leeches?

Glossiphoniid leeches provide an ideal group of animals for the study of parental care because of the diversity in parental care found within one family, reducing the problems of studying distantly related and often very different animal groups (i.e. reptiles to mammals). In addition, leeches can be easily maintained in the laboratory and studied over their entire life cycle (glossiphoniids go from egg to adult within four to six months) and several generations can be studied in a relatively short period of time resulting in relatively quick data acquisition. Glossiphoniid leeches can also be studied without having to worry about large study areas (they are quite happy in small take-away containers) and do not have many ethical problems associated with their study. Hermaphroditism in leeches also offers a means of separating male/female evolutionary conflicts over parental care from the selective pressures for care per se. Thus, this group provides a potentially rich source of experimental material for evolutionary study.

Fredric R. Govedich, Bonnie A. Bain, Lauryne J. Grant, George D. Cunningham and Martin Burd
School of Biological Sciences
Monash University
Clayton VIC 3800

Further information:

Clutton-Brock, T.H. 1991. The evolution of parental care. Princeton: Princeton University Press.

Davies, R.W., McLoughlin, N.J. and Oosthuizen, J.H. 1997. The life-cycle and feeding of the African freshwater leech Helobdella conifera (Glossiphoniidae). South African Journal of Zoology 32:1-4.

de Eguileor, M., Daniel, S., Giordana, B., Lanzavecchia, G. and Valvassori, R. 1994. Trophic exchanges between parent and young during development of Glossiphonia complanata (Annelida, Hirudinea). Journal of Experimental Zoology 269:389-402.

Govedich, F.R. and Davies, R.W. 1998. The first record of the genus Helobdella (Hirudinoidea: Glossiphoniidae) from Australia, with a description of a new species, Helobdella papillornata. Hydrobiologia 389:45-49.

Kutschera, U. 1989. Reproductive Behaviour and Parental Care of the Leech Helobdella californica (Hirudinea: Glossiphoniidae). Zoologischer Anzeiger 222:122-128.

Kutschera, U. 1992. Reproductive Behaviour and Parental Care of the Leech Helobdella triserialis (Hirudinea: Glossiphoniidae). Zoologischer Anzeiger 228:74-81.

Kutschera, U. and Wirtz, R. 1986a. Reproductive Behaviour and Parental Care of Helobdella striata (Hirudinea, Glossiphoniidae): a leech that feeds its young. Ethology 72:132-142.

Kutschera, U. Wirtz, R. 1986b. A leech that feeds its young. Animal Behaviour 34:941-942.

Mock, D.W. and Parker, G.A. 1997. The Evolution of Sibling Rivalry. Oxford: Oxford University Press.

Sawyer, R.T. 1986. Leech biology and behaviour (volumes I-III). Oxford: Oxford University Press.

leeches


Helobdella papillornata, a glossiphoniid leech that cares for its young.
Left: Ventral surface of parent showing attached eggs.
Right: Dorsal surface of adult with young peeking out from under the parent.


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