FNZ 42 - Aphodiinae (Insecta: Coleoptera: Scarabaeidae) - Biology and biogeography
Stebnicka, ZT 2001. Aphodiinae (Insecta: Coleoptera: Scarabaeidae). Fauna of New Zealand 42, 64 pages.
( ISSN 0111-5383 (print), ; no. 42. ISBN 0-478-09341-1 (print), ). Published 15 Jun 2001
Aphodiines occur worldwide, and are often common in various areas ranging from lowlands to the alpine zone and from woodlands to deserts. Most of the species live in open forest clearings, pastures, meadows, and steppes or semi-desert terrains, and occasionally in wooded areas. Species from a number of genera belonging to several tribes have adapted to the xeric environments of coastal and inland sand dunes or alkaline mud flats. The biology and ecology of the group is so diverse that few generalisations can be made.
A salient feature of the natural history of Aphodiinae, both larvae and adults, is connected with the soil. The commonly used name "dung beetles", is somewhat misleading in that only some taxa in this subfamily are at all frequently collected in dung. Although most temperate aphodiids are coprophagous and breed in the dung of herbivorous mammals, a great number of species are saprophagous in the adult stage, feeding on decomposing plant material. In temperate regions only a small number of species scattered through several genera are commonly found breeding in decaying vegetation, though the fauna found in leaf litter in the tropics is much more diverse. The adaptability of aphodiines to a wide range of diets has led to the invasion of many specialised habitats. Some species of Aphodius are kleptoparasitic, breeding in the brood balls of nest-building Scarabaeoidea, some others live in the burrows of small mammals, and in the above- ground nests of birds; many species of Ataenius and Saprosites are commonly found in decaying vegetation, in rotten wood, and under loose bark. Certain genera of the Australian and Neotropical tribes have many species that are known to be myrmecophiles and termitophiles, living in more or less close harmony with their hosts, for example members of the tribes Corythoderini (Balthasar 1964, Tangelder & Krikken 1982), Stereomerini (Howden & Storey 1992), Lomanoxiini (Stebnicka 1999b), and Eupariini (Woodruff & Cartwright 1967, Wojcik et al. 1977, Stebnicka 1998a, 1999a) have been observed with the termites Odontotermes and with the ants Atta, Solenopsis, and Acromyrmex. Many species exploit the colonies only occasionally, functioning as temporary nest commensals; however, no definite evidence is available to determine if they are synechthrans (unwelcome guests), synoeketes (unnoticed or tolerated guests), or symphiles (true guests). Some myrmecophiles fit more than one of the above categories at different times. Some species are dependent on their hosts during part or all their life cycles. The peculiar morphological features of these beetles, such as trichomes, exudatoria, mycangial structures (Stebnicka 1999c), and presence of the exocrine glands, often indicate their connections with social insects. Flightlessness accompanied by shortening or even loss of the wings, and reduction or loss of the eyes are widespread, and in some of the liquid-feeding symphilic beetles, degeneration of the mouthparts, e.g., Corythoderini. The latter morphological regression suggests the presence of trophallaxis -- an exchange of liquid food between the beetles and their hosts. The gradually increasing degree of behavioural integration with the host society constitutes the most obvious of the evolutionary pathways.
To sum up, the two main types of food resource used by the Aphodiinae are herbivore and omnivore dung and decaying vegetation. The species can be divided into two groups according to their diet and the form of the mouthparts of the adults: saprophages and coprophages.
Saprophages feed upon dead and decaying plant material that includes leaf litter and moss in forest and scrub lands, logs and tree stumps, rotting fruits, nuts, mushrooms, fallen flowers, compost, and occasional accumulations of flood debris and piles of grass cuttings. Saprophages are distributed around the world according to factors such as type of vegetation, its state of decay, amount of free water in the soil, climate, and other conditions. The saprophages have been divided into two groups (Stebnicka 1985; Cambefort 1991; Stebnicka & Howden 1995, 1996). Species adapted for "hard saprophagy", using hard organic substances, for example dead wood, leaf litter, mushrooms, and spores, and species adapted for "soft saprophagy", using semiliquid and liquid contents of decaying vegetation, for example, vegetable juices, dissolved albumenous substances, and/or bacterial albumens in decaying humus. The members of the first category, e.g., tribe Aegialiini: Stebnicka 1977, 1981, 1985; and Stebnicka & Howden 1995, have not been found in New Zealand. The second category includes most species of Saprosites, Phycocus, Proctophanes, and Ataenius.
Coprophages feed upon various fractions of excreta and all are adapted to "soft saprophagy". They are found in nearly all kinds of dung. Large herbivores eat huge quantities of grass and other vegetation, and some of this passes through the digestive system without being digested; in addition the dung contains various digestive juices, albumenous substances, fats, carbohydrates, mineral salts, vitamins, and also traces of other substances including bacterial albumens. The excreta of omnivores, e.g., man and pigs, is also often used, whereas droppings of carnivores are only occasionally visited. Through specialisation to particular ecological conditions, such as the abundance of rodents in the semi-deserts and deserts of the Old and New World, some species have become adapted to the use of the pellets of rodents. The indigenous Australian species of Podotenus (Stebnicka & Howden 1994, 1995) are attracted to human and bovine excreta; however, they mostly depend upon the pellet-like dung of marsupials. Some species are attracted in small numbers to carrion. The true coprophages include most species of Aphodiini, some Eupariini and Psammodiini, and some members of other tribes.
Generally, the climatic conditions of the environment and the microclimatic conditions of the soil restrict dung beetles to certain habitats. It is obvious that some adults of typical saprophages and coprophages have a mixed diet. For example, the adults of a given species imbibe the liquid that seeps from vegetable masses undergoing fermentation even though some individuals also occasionally consume the liquid contents of dung or exhibit other feeding habits, such as consuming various waste materials discarded by ants and termites.
The larvae of all species of aphodiines have mouthparts always of the biting type, and are able to process almost all kinds of food. Development takes place entirely in the soil, under or inside various kinds of dung, or in decaying vegetation. The females lay 20-25 eggs on average and do not look after their offspring. The majority of species have two generations per year, which means that their development cycle lasts less than a year. However, the emergence pattern is very variable and irregular, since the yearly number of generations in a given area depends on climate and on the duration of the growing season.
The distribution of many species has lost its continuous character, some of them are absent from the industrialised areas of the world. Chemicals penetrating the soil in rainwater exert a negative effect on the mortality of insects, especially at the earlier stages of development, and subsequently cause a restriction, or even total extinction of populations in a particular area.
The Aphodiinae have a bipolar geographical distribution with a few typically Laurasian tribes and several Gondwanan ones. There are also intermediate, relict tribes and genera. One of the two largest tribes, the Eupariini, is basically Gondwanan and saprophagous, whereas the Aphodiini are mostly coprophagous and are most conspicuous in temperate biomes of the northern hemisphere. It may be assumed that Aphodiinae have probably differentiated in Laurasia and Gondwana after the split up of Pangea. I suggest the beetles may then have diverged into two main sister groups, of which only the older, southern members of the Eupariini have retained a typical Gondwanan distribution. These groups may originally have had saprophagous feeding habits in tropical forests, where they probably turned to the dung of small primitive mammals that were forest dwellers (Cambefort 1991)
The current fauna of Aphodiinae in New Zealand consists of two elements: indigenous species, and species that have been accidentally introduced, mainly from Australia. How does this equate with the known distribution within and outside New Zealand of the species known from this country? Of the twenty species here recognised from New Zealand, nine are indigenous and it is possible to draw some conclusions from their systematic relationships.
Species known outside New Zealand
The eleven species known also from outside New Zealand are as follows:
Aphodius granarius (L.) and A. lividus (Ol.). Cosmopolitan, anthropogenic species with a wide range of edaphic and climatic tolerances, transported from Europe to all continents by man. Their closest relatives of the subgeneric-groups Calamosternus, Nialus, and Liothorax, occur in the Palaearctic.
Acrossidius tasmaniae (Hope). Distributed in Australia and Tasmania, closely related to the other three Australian species of Acrossidius (Stebnicka & Howden 1995); relationships of the species are unclear.
Proctophanes minor (Blackb.) and P. sculptus (Hope). Known from Australia and Tasmania, belong to a compact group of eight Australian species (Stebnicka & Howden 1995); their tribal relatives occur in Africa.
Australaphodius frenchi (Blackb.). Decidedly an afrotropical species introduced to Australia and Tasmania (Stebnicka & Howden 1995) and to Chile (new record); its congeners occur in Africa.
Parataenius simulator (Har.). Neotropical species introduced to various countries including Europe (Portugal), southeastern United States, and Australia; at least five closely related species of Parataenius occur in South America.
Ataenius picinus (Har.). Nearctic-Neotropical species, widely distributed throughout Pacific Islands to Australia; its close relatives occur in South and North America.
Ataenius brouni (Sharp). Species known from eastern Australia and Tasmania; it has clear affinities with the West Australian species A. nudus Blackburn.
Saprosites mendax (Blackb.). Australian species distributed in southeastern areas of Australia including Tasmania, introduced to Europe (England); it is close to the sympatric S. nitidicollis (Macleay).
Tesarius sulcipennis (Lea) [See Remarks at the description, p. 23]. A species known from Tasmania, most probably introduced to the Chatham Islands; its close relatives occur in Australia, e.g., Leiopsammodius newcastleensis Stebnicka & Howden (1996) described from sand dunes in New South Wales.
If we leave out of consideration the two cosmopolitan species of Aphodius, a Gondwana character is evident in the origin and distribution of all the species known outside New Zealand.
Phycocus and Saprosites both have indigenous species in New Zealand.
The monospecific genus Phycocus represents an old element and may be considered as a typical relict, widely distributed in New Zealand including the Chatham Islands and introduced to Tasmania. It seems likely that the monotypic genera are actual relicts of otherwise extinct lineages, whereas some of the other genera may represent polyphyletic lineages resulting in artificial assemblages of non-related species. Phycocus graniceps Broun shares some character states with Tesarius sulcipennis and Leiopsammodius newcastleensis, however, a possible convergence of characters complicates the question of affinities, for example, loss of hind wings with resultant morphological changes is common, as are obvious adaptations to similar habitat, in this case coastal sand dunes.
The genus Saprosites belongs to a group of related genera distributed in the Southern Hemisphere and containing the Neotropical Passaliolla Balthasar (Stebnicka 2000a) and Iguazua Stebnicka (1997), and the Asian-Australian Cnematoplatys Schmidt (Stebnicka & Howden 1997, Stebnicka 1998b). The New Zealand Saprosites species-group is morphologically very close to the tropical and subtropical groups of the genus. Based on morphological similarities and differences the New Zealand species can be split into two groups: (1) exsculptus, distans, and raoulensis; (2) communis, fortipes, sulcatissimus, watti, and kingsensis. Each group has probably evolved in New Zealand from a different ancestral colonising species. The members of group (1) appear to have close congeners in South America (Stebnicka 2001, in press), those of group (2) seem to have their closest relatives in Australia. The endemic species on the outlying islands share a large number of character states with those of the North and South Islands and are undoubtedly New Zealand derivatives.
Saprosites is seemingly one of the oldest taxa of Eupariini. Crowson (1981) assumed, that the archetypal coleopteran structure -- a somewhat flattened form with relatively short legs, and non-projecting coxae and short antennae -- is related to the style of insect life, with the species habitually taking refuge under loose bark of dead trees. The species of Saprosites live in moss, leaf litter, and in the dead, rotten trunks of many tree species. They are good examples of the "soft saprophagy" life style, with adults probably feeding on the liquid fractions of rotten wood.
Since the more primitive species or groups are likely to retain the most primitive characters it is important to know where the most primitive forms are likely to be found. New Zealand and Australia with neighbouring archipelagos, and to a lesser degree, South America, are great reservoirs of primitive types. Outside of these areas primitive groups may be widely but discontinuously distributed, frequently with highly localised, distantly related species. The New Zealand fauna of Aphodiinae is closest to that of Australia with connections to the Pacific Islands, Indonesia, Southern India, East Africa, Madagascar, and South America. The oldest forms probably arrived in the present New Zealand before the opening of the Tasman Sea 80 million years ago, and in all probability in the late Jurassic after the Rangitata Orogeny, when the present New Zealand formed part of a greater land mass connected to the rest of Gondwana (Stevens 1980). In the Cretaceous New Zealand was joined to West Antarctica (Marie Byrd Land) and fronted the broad Pacific, whereas Australia was joined to East Antarctica (Wilkes Land) and was situated in the lee of Africa-Madagascar-India. New Zealand thus became a big land mass connected to other parts of Gondwana, and could receive plant and animal immigrants from these sources. It has been forested throughout most of its history and has been an archipelago since the Late Cretaceous (Raven & Axelrod 1972). Much of New Zealand, which was previously forested, is now grassland, especially in the North Island. Clearing forest and converting it to pasture caused a local loss of the indigenous forest fauna (Watt 1977). It seems likely that the existing native species represent only a fraction of the ancient fauna. There was probably a great deal of extinction of warmth-adapted groups during the Pleistocene (Fleming 1975), and the New Zealand fauna of Aphodiinae may have been considerably less fragmented during the Tertiary than it is now. The gaps in distribution could indicate extinction resulting from climatic or geological changes, from contemporary destruction or severe modification of native habitats, or from unsuccessful competition with invading species.