In Caves and Cave Like Habitats

Cockroaches are well represented in caves throughout the tropics and subtropics, from 30°N to 40°S of the equator; they are uncommon in temperate caves (Izquierdo and Oromi, 1992; Holsinger, 2000). Except for rare collections of Arenivaga grata and Parcoblatta sp., no cave cockroaches occur in the continental United States (Roth and Willis, 1960; Peck, 1998). The biology of cave-dwelling cockroaches has been studied most extensively in Trinidad and Australia. In Guanapo Cave in Trinidad, Eu-blaberus distanti is dominant, with Blab. colloseus and Xestoblatta immaculata also found (Darlington, 19951996). These three species, as well as Eub.posticus, are also found in the Tamana Caves (Darlington, 1995a). Six cockroach species are reported from caves of the Nullar-bor Plain of southern Australia: Polyzosteria mitchelli,

Polyz. pubescens, Zonioploca medilinea (Blattidae), Neo-temnopteryx fulva, Trogloblattella nullarborensis, and Para. rufa (Blattellidae). Three are considered accidentals, two are facultative, and one is an obligate cavernicole (Richards, 1971). Cockroaches in the family Nocticolidae are consistent inhabitants of caves throughout the Old World tropics (Stone, 1988; Deharveng and Bedos, 2000). Of the approximately 20 species in the widely distributed genus Nocticola, most are cavericolous, a few are epigean or termitophilous, and a few can be found both inside and outside of caves (e.g., Alluaudellina himalayensis) (Roth, 1988; Roth and McGavin, 1994). Juberthie (2000a) estimated that worldwide, 31 cockroaches species are known to be obligate cavernicoles, but additional species continue to be described (e.g.,Vidlicka et al., 2003). Table 3.3 gives examples of cave cockroaches; others are discussed in Asahina (1974), Izquierdo et al. (1990), Martin and Oromi (1987), Martin and Izquierdo (1987), Roth and Willis (1960), Roth (1980, 1988), Roth and McGavin (1994), and Roth and Naskrecki (2003).

It is often difficult to label a given species as a cave cockroach for two reasons. First, many of the described species are based on few collection records. Second, the term cave usually refers to an underground space large enough to accommodate a human, but grand expanses such as these are just a small part of the subterranean environment (Ruzicka, 1999). The limits of the hypogean realm are hard to define because cave habitats grade into those of the edaphic environment via smaller-scale subterranean spaces such as animal burrows, tree holes, hollow logs, the area under rocks, and other such dark, humid, organic living spaces. Cockroaches found in many of these non-cave habitats occasionally or consistently exploit caves. Those that are considered "accidentals" are only rarely collected in caves. Polyz. mitchelli, for example, is a large ground-dwelling epigean Australian species that has also been taken in caves (Roach and Rentz, 1998). On the other hand, those species that typically inhabit cave entrances may venture outside the cave if the humidity is high enough (e.g., Para. rufa—Richards, 1971). Among the cockroaches taken in a range of subterranean-type habitats is the Asian species Polyphaga aegyptiaca, found in bat caves, under decaying leaves, and in cliffs along ravines (Roth and Willis, 1960), and X. immaculata, Eub. distanti, Blaberus giganteus, Blab. atropos, and Blab. crani-ifer. The latter are all considered cave cockroaches,but are also collected from under decaying litter, in epiphytes, inside rotting logs, and in the rot holes and hollows of trees, particularly those that house bats (Darlington, 1970; Fisk, 1977). Perry (1986) described dozens of adult Blab. giganteus in a tree hollow "all sitting, as sea gulls on a beach, evenly spaced and facing upward." Blatta orientalis, Blattella germanica, and P. americana have all been found in caves, as well as in buildings, wells, sewers, steam tunnels, and mines 660 m below the surface (Roth and Willis, 1960; Roth, 1985) (Fig. 3.8). In one sense, however, these human-made, non-cave habitats may be considered vertebrate burrows. Cockroaches exhibiting morphological correlates of cave adaptation such as elongated appendages and the loss of pigment, eyes, and wings are generally restricted to cave habitats, but even these can be found elsewhere. A species of Australian Nocticola with reduced eyes and tegmina and no wings lives beneath rotting logs (Stone, 1988). The troglomorphic Symploce mi-cropthalmus lives in the mesocavernous shallow stratum of the Canary Islands, but is also found under stones in humid areas (Izquierdo and Medina, 1992).

Individual caves are commonly divided into zones,

Table 3.3. Examples of cave-dwelling cockroaches.

1. Occur in caves sporadically, and sometimes become established there; show no morphological characters specifically associated with cave dwelling.

Examples: Blattidae: Periplaneta americana, Polyzosteria mitchelli; Blaberidae: Pycnoscelus indicus, Pyc. surinamensis, Blaberus colosseus

2. Habitually found in caves, but are able to live in or outside of caves; they show no characters adaptive for cave dwelling.

Examples: Blattidae: Eumethana cavernicola; Blattellidae: Blattella cavernicola; Blaberidae: Blaberus craniifer, Eublaberusposticus,Aspiduchus cavernicola

3.Cannot live outside of caves and show marked morphological specializations for the cave habitat (obligate cavernicoles or troglobites).

Examples: Blattidae: Neostylopyga jambusanensis; Blattellidae: Neotrogloblattella chapmani, Loboptera anagae, L. troglobia, Paratemnopteryx howarthi, Para. stonei, Trogloblattella chapmani; Nocticolidae: Alluaudellina cavernicola, Typhloblatta caeca, Nocticola simoni, Noc. australiensis, Noc. bolivari,Noc. flabella, Spelaeoblatta thamfaranga

Fig. 3.8 Periplaneta sp. in a sewer manhole in Houma, Louisiana. From Gary (1950).

with each supporting a different community (Juberthie, 2000b). The twilight zone near the entrance is closest to epigean conditions and has the largest and most diverse fauna. Next is a zone of complete darkness with variable temperature, and finally in the deep interior a zone of complete darkness, stable temperature, and stagnant air, where the obligate, troglomorphic fauna appear (Poulson and White, 1969). The degree of fidelity to a zone varies. While the Australian Para. rufa is found only from the entrance to 0.4 km into a cave, Trog. nullarborensis is found from the entrance to 4.8 km deep; it roams throughout the cave system and is one of the few troglomorphs recorded from the twilight zone (Richards, 1971). Eu-blaberus posticus and Eub. distanti may segregate in caves according to their particular moisture requirements. The former prefers the moist inner sections of caves, while the latter is more common in drier guano (Darlington, 1970). The habitable areas of caves, and consequently, populations of cave organisms, are dynamic—they move, expand, and contract, depending on climate and on pulses of organic matter (Humphreys, 1993). After an exceptionally cool night in Nasty Cave in Australia, for example, a common Nocticola cockroach could not be found and was thought to have retreated into cracks during the unfavorable conditions (Howarth, 1988). Initially a small species in the subfamily Anaplectinae was sporadically seen in a Trinidadian cave, subsequently formed a thriving colony, then was wiped out when the cave flooded. It did not reappear (Darlington, 1970).

Caves with a source of vertebrate guano support very different cockroach communities than caves that lack such input. Guano caves typically contain very large numbers of few cockroach species able to maintain dense populations and exploit the abundant, rich, but rather monotonous food bonanza (Darlington, 1970). Examples include a population of more than 80,000 Gyna sp.

in a South African cave (Braack, 1989), more than 43,000 Eub. distanti in just one chamber of a cave in Trinidad (Darlington, 1970) (Fig. 3.9), and Pycnoscelus striatus found at approximately 2000-3000/m2 in the Batu Caves ofMalaysia (McClure, 1965).A similar scenario is that of approximately 3000 P. americana /m2 in a sewer system more than 27 m beneath the University of Minnesota campus (Roth and Willis, 1957). In guano caves, the distribution of cockroaches usually coincides with that of bats and their excrement (Braack, 1989). Some species are consistently associated with bat guano, wherever it is found. One South African Gyna sp. was present in all bat-inhabited caves and cave-like habitats, including the roof of a post office (Braack, 1989).

Highly troglomorphic cockroach species generally support themselves on less rich, less abundant food sources. Trogloblattella chapmani is typically found remote from guano beds in passages floored by damp sticky clay or silt (Roth, 1980). Metanocticola christmasensis is associated with the often luxuriant tree root systems that penetrate caves (Roth, 1999b), but their diet is unknown (Roth, 1999b). Troglomorphic cockroaches tend to move

Fig 3.9 Habitat stratification in Eublaberus distanti in Gua-napo Cave, Trinidad. (A) Adults on walls of cave; (B) nymphs on surface of fruit bat guano. Photos courtesy of J.P.E.C. Darlington.

very slowly (e.g., Nocticola spp.—Stone, 1988; Loboptera troglobia—Izquierdo et al., 1990), and produce few eggs. The oothecae of Alluaudellina cavernicola contain only four or five eggs (Chopard, 1919) and those of Nocticola ( = Paraloboptera) rohini from Sri Lanka contain just four (Fernando, 1957). Among the seven species of Loboptera studied by Izquierdo et al. (1990) in the Canary Islands, reductions in ovariole number paralleled the degree of morphological adaptation to the underground environment. The least modified species had 16-18 ovarioles, while the most troglomorphic had six ovarioles. It is unknown whether troglomorphic cockroaches exhibit the increased developmental time and lifespan, decrease in respiratory metabolism, and loss of water regulatory processes found in many other cave-adapted animals (Gilbert and Deharveng, 2002).

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