ETHOLOGICAL REPRODUCTIVE ISOLATION BETWEEN TWO POSSIBLE SYMPATRIC SPECIES OF GRAMMOSTOLA (ARANEAE: THERAPHOSIDAE) IN BUENOS AIRES, ARGENTINA.

FERRETTI NELSON; COPPERI SOFÍA; POMPOZZI GABRIEL; PÉREZ-MILES FERNANDO

Alexandroupoli, Grecia

Congreso; 25th European Congress of Arachnology; 2009

Democritus University of Thrace Department of Molecular Biology and Genetics

At the south of the Buenos Aires province are present two species of tarantulas, Grammostola doeringi Holmberg 1881 and Grammostola schulzei (Schmidt, 1994). Grammostola schulzei is a spider that inhabit burrows made always under stones in rocky hills, in Sierra de la Ventana (38º 07’ 63” S 61º 47’ 30” W), Ventania, while Grammostola doeringi is present at the outskirts of Bahía Blanca (38° 44’ 30” S 62° 12’ 31” W), where it lives in burrows made in open field at the pampas. Recently, some individuals of Grammostola schulzei were found living near Bahia Blanca and individuals of Grammostola doeringi in Sierra de la Ventana. These findings suggested us that must exist an overlapping zone in which the species are sympatric. In addition, the sexual period of these species overlaps in time; walking males can be found during October – December (late spring and early summer in South Hemisphere). Reproductive isolation mechanisms are especially important in sympatric and synchronic species since they provide insights into the process speciation in singular conditions. Moreover, differences in reproductive isolating traits are expected to be greater in sympatry than in allopatry. This pattern of sympatric divergence arises from selection against the adverse consequences of hybridization between sympatric species. In Theraphosidae, the reproductive isolation was examined under laboratory conditions for three populations of Grammostola mollicoma and Grammostola iheringi occurring in Uruguay, where no isolation was found on G. mollicoma due to their poor knowledge on distribution of these populations, but G. iheringi showed an effective ethological reproductive isolation. The main objective of this work is to test if the species mentioned have ethological mechanisms of isolation under laboratory conditions. We studied male’s courtships and females responses in conspecific and heterospecific encounters. We used five males and eight females of G. doeringi and four males and ten females of G. schulzei. Individuals were randomly assigned to pairs. So, males of the two species were in contact with conspecific and heterospecific females in all possible combinations. The interactions between individuals were carried out in cages of 30 x 35 and 30 cm high, with a layer of soil of 10 cm deep and a burrow was excavated against the glass wall allowing for observation. Encounters were videotape and analyzed. Males courted on silk tracks of conspecific and heterospecific females. Both males of G. doeringi and G. schulzei showed approximately same frequencies of bouts in all interactions during courtship. However G. schulzei displayed palpal drumming and palpate, while G. doeringi only palpated. Grammostola doeringi performed more leg tapping and palpating with conspecific than with females of G. schulzei. On the other hand, G. schulzei courted more vigorously to females of the other species than conspecific. None of females called males, and the acceptation of males for mating was given by the female leaving the burrow, raising her body and opening fangs. Usually mating takes place outside the burrow due to spatial constrains. When heterospecific males entered to the burrow, females beat them with the first pair of legs and males escaped without injuries. Moreover, sometimes females leaved their burrows when confronting a heterospecific male; then females raised their bodies but didn´t open her fangs, so that males failed to clasp and moved away. On those cases, females didn´t reach the immobile condition and usually attacked males (3 females of G. schulzei) and even predated them (2 females of G. schulzei). Females of G. doeringi were more passive and didn´t showed aggression. We registered one interspecific mating, with a male of G. doeringi and a female of G. schulzei, with regular posture and insertions. Usually an ethological isolation mechanism operated after physical contact, although it could exceptionally fail. In this case, the cost in energy, time and risk is high for the couple and especially for female. An alternative interpretation of this failure could be a female strategy for predation on heterospecific males.