Comments on the Species Concept in Some Australian Anisops Spinola (Hemiptera: Notonectidae)
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https://doi.org/10.24199/j.mmv.1978.39.08 7 July 1978 COMMENTS ON THE SPECIES CONCEPT IN SOME AUSTRALIAN ANISOPS SPINOLA (HEMIPTERA: NOTONECTIDAE) By I. Lansbury Hope Department of Entomology, University Museum, Oxford Introduction tralian species with reliable k spof characters Twenty-five species of Anisops are recorded are stall Kirkaldy; calcaratus Hale; nasuta Fie- from Australia and Tasmania, 16 are endemic. ber; semita Brooks; and tahitiensis Lundblad. the A few species are taxonomically confusing as Of remainder, thienemanni Lundblad; no- ditlata and canaliculate Brooks are easily they occur in more than one form. Anisops is recognized by rostral compared with Bttenoa Kirkaldy which replaces abnormally shaped prongs. Anisops in the New World. The characters used by Brooks (1951) to The species concept is discussed, especially separate fall of those with an extra-Australian distribution species into two categories (1) of the capsule and the which tend to be superficially distinct at the morphometries head periphery of their range. pronotum; (2) presence of grooves, ridges prolongations of the especially Figures and short descriptions are given of or head capsule the facial tubercle. Secondary sexual charac- little known species from New Guinea which ters with combinations of the primary features may eventually be found in Australia. Finally are reworked to enable species to be keyed a new species is described from Lihir, Bis- marck Archipelago. out. The measurements of the head and prono- tum are not easy to make as the structures are Species Concept nearly all convex. The chaetotaxy of the male front leg, number of pegs in the stridulatory Alpha taxonomy row and distribution of spines and setae on To understand the problems posed by vari- the front tibia and tarsus are used. The ros- ous species of Anisops, it is necessary to con- tral prongs which are projections borne either sider the species concept in the genus. With few side of the third rostral segment are also im- exceptions, only the males can be named with portant. reasonable certainty. Attempts by Sweeney (1965) and Lansbury Wing polymorphism (1969) to devise reasonably easy keys to the The terminology used to indicate if an Ani- Australian Anisops have not been completely sops can fly or not is rather confusing. No successful. The occasional failure of my 1969 problem arises over the term macropterous, key is caused by trying to key out forms of but brachypterous can be misleading. Ail Aus- species which were not available to me when tralian Anisops have fully developed fore the key was prepared. The key couplet re- wings and hind or metathoracie wings. Despite ferring to the comparative width of the head the presence of wings, most species produce to the pronotum has proved unreliable when forms with the wing musculature undeveloped, dealing with species which vary in the degree in its place parenchymatous tissue. Young of development of the flight musculature. (1962) uses the term 'normal' for individuals There are over one hundred described and capable of llight and 'flightless' for those which seemingly valid species of Anisops, some of although possessing full sized wings, have not them with a widespread distribution. The developed (light muscle. characters used to divide up the genus into The term 4 brachyelytrous' has been sug- manageable proportions vary greatly in their gested, although possibly quite suitable, some reliability. Structural peculiarities of the head confusion may arise as this term is also applied and rarely the pronotum easily distinguish a to the Staphylinidae and Dermaptcra with their small number from most of the genus. Aus- characteristic short elytra, a condition not oc- 101 io: r. LANSBURY earring in Anisops. To avoid confusion, the In B. lirtinocastris Hungerford and other terminology of Young (1962) is followed in species, both sexes of the flightless forms have these notes. the head as wide or wider than the pronotal The normal forms with fully developed flight humeral width, normal forms of both sexes musculature are easily recognized by the pig- have the head narrower than the humeral mented scutellum, the clavus and corium also width. Truxal (1953) describing the wing poly- coloured, most commonly black, brown, red morphic forms of limnocastris found that the or yellow, usually a subtle combination of two scutellum of the normal form was longer than or three colours. The metanotum is black or the median length of the pronotum, that of the dark brown. Flightless forms (always with flightless form clearly shorter. These differen- fully developed metathoracic wings in Austra- ces have not been found so far in Anisops. lian species) have hyaline scutellums, the dor- Colour sal pigmentation showing through, likewise the It is the of clavus and corium. The metanotum is not pig- not known how much colour Ani- mented, but occasionally dark brown at the sops species can vary. Young (1962) found a wing bases. The following descriptions are direct correlation between colour and flight taken from Young (1962) and refer to assimi- musculature. There is some evidence that in circumstances Anisops exhibit lis and wakefieldi White, both endemic to New some a pheno- Zealand. The macropterous form of both sexes menon rather better known in the Corixidae have the lateral margins of the pronotum di- (see deanei). Specimens from turbid water with vergent. The males of the brachypterous forms a peaty or dark substrate frequently have a have more-or-less parallel sided pronotums and much larger area of the hemelytra with dark females with slightly divergent pronotums. A brown transverse markings, the pronotum is check of Brooks (1951) and Lansbury (1964) often more heavily pigmented. The same spe- shows that they often described two colour cies of corixid from a sandy or gravel substrate forms of a species but did not comment on the are much paler. The significance of colour in shape of the pronotum. A further complication Anisops where it impinges on food gathering has been found in a number of species which and its role in enabling Anisops to merge with are isolated from the rest because the head is the background are poorly documented. The as wide or wider than the pronotal humeral differences noted by Young (1962) refer al- width, these are: evansi Brooks (Tasmania) most exclusively to the colour of the scutellum. robusta Hutchinson (E. Africa) lencothea Esa- The pale flightless Anisops with little dorsal ki (Samoa and elsewhere) doris Kirkaldy pigmentation may be difficult for a predator to (Australia) tasmaniaensis Brooks (Tasmania) locate visually, the normal form with a pig- philippinensis Brooks (Philippines and else- mented scutellum and intensified colouring of where) and assimilis. Young's (1962) descrip- the hemelytra may be easier for a predator to tion of assimilis differs from Brooks, the head see. Both forms would be equally at risk viewed irrespective of the form is always narrower from any position sub-surface when ascending to the surface to than the pronotal humeral width, it seems to renew their gas supply or at risk from predators which use other senses be a general rule in Anisops that the lateral than sight to locate their prey. Bayly, Ebsworth and margins of the pronotum of flightless males are Wan (1975) present data from which it can be more-or-less parallel sided, therefore the taxo- inferred that within closed systems such as nomic value of the head-pronotal width is of exist on Fraser Island, Qld., that fish and limited use in those species which have more water-bugs are mutually exclusive. They pos- voluminous eyes. Series of evansi from Tas- tulate that either the fish eliminate the bugs and the mainland show both forms to mania be by feeding on them, or the fish out-compete present, where females can safely be associated the bugs for the available food supply. Young's with males, the head is always narrower than (1962) data on assimilis shows that both forms the humeral width. were found in almost equal numbers. The num- AUSTRALIAN ANISOPS 103 ber of habitats where only the normal form alike Anisops, one of the main differences be- were found was almost the same as the flight- ing that the male Buenoa has two segmented less form. The total number of habitats with front tarsi, whereas Anisops males have one- both forms present being just over double the segmented tarsus. It is felt that the behaviour of number of those where only one form was Buenoa and Anisops are probably rather simi- present. Anisops wakefieldi differed, the nor- lar. In laboratory experiments it has been mal form was ten times more common than the found that B. limnocastris males will pair with flightless and four times as many habitats were macrotibialis Hungerford females, the Fj gen- populated by the normal form compared with eration are sterile, males morphologically in- the flightless form. Both species were found termediate, their acoustical behaviour similar together in 'swarms', assimilis having a to that of their male parents. Stimson Wilcox greater tolerance of habitat types. In the more (n.d.) (1975). Truxal (1953) descriptions of the stable weedy habitats with little open water stridulatory apparatus of Buenoa species, es- wakefieldi was the dominant species. pecially the number of stridulatory pegs shows that within a species, the variation found is Genitalia less than in Anisops. Young (1962) found that The genitalia of Anisops are of very limited in assimilis males, the shape and number of value at the species level. Brooks (1951) figured stridulatory pegs was fairly constant; the size the left and right parameres but made no re- and arrangement in wakefieldi could be vari- ference to them. Young (1962) did not figure able (28 and 15 pegs respectively).