Download 1 Zoogeographical Notes on the Sciomyzidae (Diptera: Acalyptratae

Zoogeographical Notes on the Sciomyzidae
(Diptera: Acalyptratae) of the Americas
South of the United States
Larvae in many genera of Sciomyzidae (marsh flies or swale flies) are known to prey
upon freshwater or terrestrial snails (Berg, 1953, 1961, Knutson, 1973). One or more species in
18 of the 20 genera herein recorded from the Americas south of the United States (all except
Euthycerina and Teutoniomyia) are known to have snail-killing larvae (Abercrombie, 1970, Bratt
et al., 1969, Fisher and Orth, 1964, Foote, 196l, unpublished, Foote et al., 1960, Kaczynski et al.,
1969, Knutson, 1963, 1966, Neff and Berg, 1961, 1962, 1966, Valley, 1974, unpublished, Zuska,
unpublished). Academic interest in these specialized predators, and potential practical
importance of the results of their predation, have stimulated considerable effort to collect and
rear the Sciomyzidae. Collecting in the Americas south of the United States has led to
zoogeographic observations that support some popularly held views but differ sharply from
others.
ZOOGEOGRAPHIC GROUPS OF GENERA
The genera of Sciomyzidae that occur in the Americas south of the United States can be
classified zoogeographically in five major groups (fig. l). Group A is composed of seven
essentially Nearctic or Holarctic genera (or they are even more wide-ranging, as in the case of
Sepedon) which have extended their ranges various distances southward from the United States.
Euthycera occurs in Europe and in North America, southward to the Mexican state of Durango
(Knutson and Zuska, 1960). Tetanocera, Antichaeta (both Holarctic) and Atrichomelina
(Nearctic) have progressed southward to the latitude of Mexico City (Valley, unpublished, Foote
et al., 1960, Foote, 1961). Like Euthycera, however, they probably do not occur anywhere in the
Neotropical region. Sepedon has been recorded from many collecting sites in the Antilles,
Central America, and South America (Steyskal, 1951), but all of those records are based upon
species now referred to either Sepedomerus or Sepedonea (Steyskal, 1973). The most southern
record for any species now retained in Sepedon probably is the capture of S. praemiosa GiglioTos at Oaxaca, Mexico (Neff and Berg, 1966), near the line of demarcation commonly
recognized between the Nearctic and Neotropical regions. Hoplodictya (chiefly Nearctic) and
Dictya (with more than 20 North American and 1 European species) clearly range into the
Neotropical region. Species of both genera have been collected in the Antilles and Guatemala,
and a species of Dictya has been taken in Costa Rica and Colombia (Fisher and Orth, 1972,
Valley, 1974).
Group B comprises five genera that are confined, or very nearly confined, to the tropical
subregion of South and Central America. Species in these genera occur in the hot, humid country
at low elevations between the Tropic of Cancer and the Tropic of Capricorn, or somewhat
beyond those latitudinal boundaries where the climate characteristic of the tropical lowlands
extends beyond them. They are not found in cool climates resulting from either high altitude or
high latitude. The most widespread genus, Sepedomerus, occurs in the low marshes both east and
west of the Andes Mountains, but not in the high mountain valleys. One species (S. macropus
(Walker)) ranges northward through Central America and the Gulf coastal plain of Mexico to
Brownsville, Texas, and southward in the marshes of the Pacific Coast of South America beyond
Lima, Peru (fig. 2). It and other species in this genus are common in the Greater Antilles and
Trinidad. Sepedomerus bipuncticeps (Malloch) occurs in northern South America (e.g. Cali,
Colombia) and also in southern Brazil, Paraguay, Uruguay, and northern Argentina. The
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sciomyzid fauna between the northernmost and southernmost records for this species remains
poorly known. We have indicated (fig. l) that Sepedomerus probably extends through this area,
westward to the Andes Mountains. Although this broad range is not substantiated by capture
records nearly so dense as those shown for S. macropus in Central America, no discontinuity of
climatic, topographic, or vegetational features in this vast area of tropical lowlands would seem
to suggest that the northern and southern populations of S. bipuncticeps are disjunct.
Like Sepedomerus, Sepedonea also extends southward to Buenos Aires and curves
around the northern end of the Andes to start southward in the tropical marshes west of the
continental divide. However, Sepedonea has not been taken on the Pacific slope south of Cali,
Colombia; it is not found in the Greater Antilles; and its known range extends northwestward on
the mainland only to the lower end of Mexico. Thecomyia is more restricted than Sepedonea,
being confined to Central America and South America east of the continental divide. Its range
extends northwestward to Guatemala, southeastward through Venezuela and the Guianas to the
south Brazilian State of Santa Catarina, and westward to the foothills of the Andes in Ecuador
and Peru (G. C. Steyskal, in manuscript). Guatemalia is known only from southern Mexico,
Guatemala, and Costa Rica. Capture records for Teutoniomyia suggest a widely disjunct
distribution. One species has been collected only in Costa Rica; the other occurs at Rio de
Janeiro and in the State of Santa Catarina, Brazil, and at Tucumán, Argentina.
Group C is made up of five genera even more strictly confined to the temperate subregion
of South America than Group B is to the tropical. Three genera range from the Pacific to the
Atlantic coast south of the Tropic of Capricorn, and two of these extend far northward in the
narrow belt of temperate climate in the Andes Mountains (fig. l). Perilimnia, the most wide
ranging genus, dominates many collecting sites in cool, humid areas from the Strait of Magellan
to the vicinity of Bogota, Colombia. Dichrochirosa has a similar range, but its northward
extension in the mountains is not known to surpass Quito, Ecuador. All seven species assigned to
Tetanoceroides occur in Chile, and all are confined to latitudes exceeding 27° south. Five species
have been collected also in Argentina, and one has been taken in Uruguay (Zuska and Berg,
1974). Shannonia and Euthycerina range southward in Chile below the coastal deserts of the
northernmost provinces. Neither is known from northern and central Argentina, where the
mountains on the Chile-Argentine boundary are high enough to constitute an effective barrier.
South of 40°S latitude, however, where the low mountain passes permit migration, species of
both genera have been collected in the Argentine province of Rio Negro, and we have taken
Shannonia also in Chubut and Santa Cruz (Kaczynski et al., 1969).
Protodictya and Dictyodes, the only genera in addition to Pherbellia that breed
extensively in both tropical and temperate subregions of South America, are placed together in
Group D. The range of Protodictya extends from Mexico through Central America, Venezuela,
and Brazil to southern Chile and Patagonia. It apparently does not include either the mountains
of Colombia, Ecuador, and Peru or the coastal marshes west of them. At least five species are
confined to tropical habitats in Central America, Venezuela, and Brazil. One species, P. chilensis
Malloch, occurs only in temperate portions of Chile and Argentina; two species, P. guttularis
(Wiedemann) and P. lilloana Steyskal, evidently breed with equal success in both subregions.
The north-to-south range of Dictyodes is much less extensive, but it is almost equally divided
between tropical and temperate subregions in southern Brazil (north to Rio de Janeiro), Bolivia,
and eastern Argentina (south to Buenos Aires and Tandil).
Group E, widely distributed through both North and South America, is represented solely
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by the nearly cosmopolitan genus Pherbellia. The distribution of this genus in the Western
Hemisphere stretches through 123 degrees of latitude — from Prudhoe Bay on the Arctic coast
of Alaska, to Tierra del Fuego. Species of Pherbellia are less common in tropical than in both
north-temperate and south-temperate zones, but they occur in scattered tropical habitats in the
Antilles, Central America, and both east and west of the Andes Mountains in South America.
We are following Steyskal (1949) in using the generic name Pherbellia in the broad
sense, although further study of this large taxon may result in its being split into several genera.
A policy of nomenclatural conservatism in this matter seems prudent until a worldwide study of
all species assigned to Pherbellia can be made. Proposed generic segregations of some European
species, made without benefit of such an extensive study, have not been adopted by subsequent
workers. For this and other reasons, we are not now adopting the generic names Notopherbellia,
Melina, and Pseudomelina, applied by Malloch (1933) and Stuardo Ortiz (1946) to the
Patagonian sciomyzid fauna. Melina Robineau-Desvoidy, 1830 is preoccupied by Melina
Retzius, 1788 (Mollusca). Other names used by Malloch and Stuardo Ortiz but not by us are
Notosciomyza (a junior synonym of Perilimnia) and Sciogriphoneura (a genus of Dryomyzidae).
DISCUSSION
Students of the Neotropical fauna have stated that South America can be divided into
sharply defined tropical and temperate subregions, the latter extending northward across the
equator in a narrow belt of high elevation in the Andes Mountains. Fittkau (1969: fig. 1, p. 643)
showed the "Andean-Patagonian" subregion protruding northward in the mountains almost up to
the equator. Kuschel (1969: fig. 1, p. 711) extended this temperate subregion even farther north
— across the equator, through Colombia, and into western Venezuela. His line of demarcation
between the "Patagonian" (temperate) and "Brazilian" (tropical) subregions (fig. 2) is based on
distribution patterns of Coleoptera in various families. It separates the ranges of the South
American Sciomyzidae remarkably well. Ten of the 12 sciomyzid genera endemic to the
Neotropical region are, with minor exceptions, confined to one subregion or the other. No
species in any of the five genera in Group C has been collected on the tropical side of that line.
Only two species in Group B, Sepedomerus bipuncticeps (Malloch) and Sepedonea lindneri
(Hendel), are known to occur on the temperate side of it, in a relatively small area of overlap
from Buenos Aires north to southern Brazil. Only the three genera assigned to Groups D and E
have extensive ranges on both sides of Kuschel's line, and most of the species even in those
genera occur only on one side, or on the other, of this line.
The sharp segregation of temperate and tropical species is illustrated by two species that
occur in close proximity over 20 degrees of latitude but have never been found together (fig. 2).
Perilimnia albifacies Becker, which has by far the greatest range of any species in Group C, is
widely distributed in lowlands as well as the mountains from the southern tip of South America
northward to approximately 25ºS latitude. North of the Tropic of Capricorn, this species is
confined to the cool intermontane valleys, but in those valleys its range extends northward
through Bolivia, Peru, Ecuador, and part of Colombia. The larva of this species is predatory on
aquatic, pulmonate snails of various genera (Kaczynski et al., 1969).
Sepedomerus macropus (Walker) is probably extending its range from a point of origin in
Central America. Although it has spread southward through the hot, humid marshes on the
Pacific coast of Colombia, Ecuador, and most of Peru, it evidently has not invaded the
intermontane valley habitats of P. albifacies in those countries. Most of the collecting sites
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shown for P. albifacies in the narrow belt of high elevation in the mountains, and most of the
sites indicated (fig. 2) for S. macropus on the narrow coastal plain west of it, are sites where we
have collected. In all of those marshes, enough effort was made to support the conclusion that
S. macropus is not present in the intermontane valleys and P. albifacies is not present in the
coastal marshes. The larva of S. macropus is also predatory on various aquatic pulmonates, but
the larvae live in different microhabitats, and their adaptations and modes of life are quite
different (cf. Neff and Berg, 1966 and Kaczynski et al., 1969).
Distribution patterns of the Sciomyzidae thus lend strong support both to the sharp
division of South America into subregions and to the northward extension of the temperate
subregion across the equator. The ranges of Perilimnia and Dichrochirosa, and their evident
conformation to ranges of the temperate species of Coleoptera studied by Kuschel, indicate that
the climatic conditions optimal to both beetles and flies extend far northward, but only in a
narrow belt of high elevation in the mountains. Additional evidence of this long, narrow
"peninsula" of temperate conditions is found in the exclusion of a tropical genus such as
Sepedomerus, which evidently surrounds it on both sides and one end, but nowhere intrudes into
it.
The Sciomyzidae also give strong support to the statement (e.g. Fittkau, 1969) that the
South American fauna is unusually rich in endemic species. In the Sciomyzidae, there is a high
proportion of endemism even on the generic level. Twelve of the 14 genera found in South
America, all genera in Groups B, C, and D, are essentially endemic to the Neotropical region.
(This counts Sepedomerus as a Neotropical endemic, although S. macropus has been collected as
far north as Brownsville, Texas.) The only genera found in the mainland of South America that
breed extensively in other zoogeographic regions are Dictya and Pherbellia. The species of
Dictya collected in Colombia and Costa Rica is a Neotropical endemic, as are most of the species
of Pherbellia found in South America. The conclusion that the fauna of South America has
developed undisturbed and well isolated from other continents seems inescapable.
Authors have reported that a high proportion of the Chilean fauna is endemic to that
country. Peña (1966) and Artigas (1970) both stated that Chile has a distinctive "fauna of its
own". Because of deserts on Chile's border with Peru and high mountain chains on her border
with Bolivia and much of Argentina, the fauna of Chile is more distinctive than that of most
continental nations having such extensive perimeters. However, the impression of high
endemism probably has been exaggerated because of limited collecting in much of Argentina. It
seems almost certain that more collecting effort, especially in southwestern Argentina, will
reduce considerably the number of species that would now be listed as Chilean endemics. The
mountains from about 40°S latitude to the southern tip of the continent are not very high, and
there the Chilean "... forests of Nothofagus and Araucaria and their associated faunas extend into
the Argentine territories ..." (Peña, 1966).
Although Tetanoceroides was considered a primarily Chilean genus, five of the seven
species are now known also from Argentina (Zuska and Berg, 1974). Seven of the eight species
of Sciomyzidae most commonly collected in the marshes near Santiago occur also in Argentina.
Judging solely on the Sciomyzidae, one would have to conclude that the endemism of Chile on
the species level is not nearly so remarkable as the endemism of Latin America, on the genus
level. For example, Protodictya chilensis Malloch is not endemic to Chile, but its genus is
endemic to the Neotropical region. The same statement can be made concerning at least nine
other Chilean species of Sciomyzidae.
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Several students of Patagonian insects (e.g. Brundin, 1966, Illies, 1969) have concluded
that their closest phylogenetic relationships are with the faunas of Australia and Hew Zealand.
These relationships in the Chironomidae seemed so strong to Fittkau that he wrote (1969), "... a
Mesozoic areal connection — at least between part of South America and Australia-New
Zealand — has become a conceptual necessity." However, we cannot see any phylogenetic
relationship between the sciomyzid fauna of Patagonia and that of Australia and New Zealand.
Only one of the five subfamilies occurs in both regions, and that subfamily (Sciomyzinae) is
practically cosmopolitan. The only genus found in both Patagonia and Australia (Pherbellia) is
represented by strikingly different species in these two regions. The Pherbellia of Australia are
obese, heavy-bodied flies with darkly pigmented bodies and wings. Their larvae habitually
pupate inside the shells of the last snails they consume (Berg, unpublished). By contrast,
Pherbellia patagonensis (Macquart) and other Patagonian species are slender flies with
immaculate wings, light pigmentation of the body, and structural characters completely different
from those of the Australian Pherbellia. Their larvae also pupate in the shells of their last
victims, but this habit has evolved several times and is found in other genera of Sciomyzini as
well as Pherbellia; it must be considered adaptive and without phylogenetic significance.
However, the North American P. humilis (Loew) is morphologically so similar to P.
patagonensis, and both are so similar to the European P. grisescens (Meigen), that both
American species were once sunk in synonymy under P. grisescens. They were resurrected as
valid species (Steyskal, 1963) only after a careful comparison of male genitalia. Perhaps
significantly, the range of P. humilis extends southward to Costa Rica; it seems that this species
might well have given rise to P. patagonensis.
The endemic Neotropical genera also show close relationships with Nearctic genera and
probably were derived from them: Sepedomerus, Sepedonea, and Thecomyia with Sepedon;
Guatemalia and Tetanoceroides with Tetanocera; Shannonia and Perilimnia with Tetanocera or
perhaps Antichaeta (but these are probably the most distinctive of the Neotropical genera and the
hardest to associate positively with any other sciomyzid genus); Protodictya and Dictyodes with
Dictya; Teutoniomyia with Dictyacium; Dichrochirosa with Pteromicra; and Euthycerina with
Euthycera. A conclusion of Darlington (1957:449) may be as applicable to the Sciomyzidae as to
the vertebrates that he wrote about: "In short, the whole existing Neotropical vertebrate fauna is a
mixture of surviving parts of an old, endemic Tertiary fauna . . . and a new fauna received via
North America." In the Sciomyzidae, the old, endemic Neotropical genera probably also came
from North America. A statement of Simpson (1943:417) seems equally applicable to the
Sciomyzidae: "Many of the earlier immigrants from North America have been in South America
long enough to develop distinctive genera (but not families) there and even the later migrants
among mammals are, as a rule, specifically distinct in the Neotropical Region."
However, we do not debate statements that the primitive Chironomidae, Plecoptera, and
Ephemeroptera of Patagonia may have their closest relatives in the Australian region. The origins
of those ancient groups are believed to go back to the Triassic, Permian, and Pennsylvanian
periods. If so, and if Gondwanaland did not divide until late Triassic or early Jurassic, those
groups may have been widespread in Gondwanaland before the rift of that early continent
occurred. However, the Sciomyzidae probably had not evolved at that time. The finding of five
species in Baltic amber (Hennig, 1965) proves that they go back to the Oligocene, but it is
doubtful if they or any other acalyptrate family arose much earlier than that. After making an
extensive study of the Diptera in Canadian amber (Cretaceous), J. F. McAlpine states (personal
communication) that he has found nothing that would qualify as a true acalyptrate. So
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postulation of a Mesozoic land bridge between Patagonia and Australia- New Zealand for the
acalyptrate Diptera would be as pointless as for the mammals, and for the same reason -- neither
group was here then to utilize it.