First report of use of land snails for Heteromys gaumeri (Rodentia: Heteromyidae) in a subdeciduous forest in Yucatán, México

S.F. Hernández-Betancourt¹, J. Gómez González¹, J. A. Cimé Pool¹, S. Medina Peralta^1,2 y C. M. Euán Canul¹

¹ Departamento de Zoología, Facultad de Medicina Veterinaria y Zootecnia, Universidad Autónoma de Yucatán Km 15.5 Carr. Mérida -Xmatkuil, CP 97100 Apdo. Postal 4-116 Itzimná, Mérida Yucatán, MÉXICO. hbetan@tunku.uady.mx

² Facultad de Matemáticas Universidad Autónoma de Yucatán, Periférico Norte tablaje 13615 Cordemex CP 97110 Yucatán MÉXICO.

Se presenta el primer registro de uso de caracoles terrestres por Heteromys gaumeri en la selva mediana subcaducifolia localizada en el Rancho Hobonil, Tzucacab, Yucatán, México. Siete por ciento de la población total (n= 789) de H. gaumeri usó caracoles que habitan en el área. Las especies fueron: Choanopoma largillierti y C. gaigei (Annulariidae), Neocyclotus dysoni (Cyclophoridae) y Drymaeus shattucki (Bulimulidae). Cincuenta y uno por ciento de las muestras de los roedores fueron hembras y el 49% machos. Los adultos representaron el 86% y los juveniles 14%. El uso de caracoles tuvo relación significativa entre sexos de los roedores y la estacionalidad (p< 0.01). Los caracoles fueron usados con mayor frecuencia en la estación de sequía por las hembras y por los machos adultos y juveniles en la de lluvias. Treinta y cinco por ciento de las hembras de la muestra que usaron caracoles estaban preñadas o lactantes. El género Choanopoma fue el más abundante y removido por H. gaumeri en ambas estaciones, mientras que Neocyclotus lo fue en la de lluvias y D. shattucki se encontró rara vez. Por lo observado consideramos que este ratón además de semillas come caracoles terrestres en esta región.

All the species of Heteromyidae family are granivorous, although some also feed on invertebrates when they are available (Reichman & Price 1993 IN: BIOLOGY OF HETEROMYIDAE 539-574). Some studies investigating the feeding habits of desert heteromyids have reported seasonal consumption of invertebrates, with the analysis of stomach contents and feces revealing invertebrate remains in more than 50% of the samples. In contrast, the diet of tropical heteromyids has been poorly documented (Reichman & Price 1993 op cit.). Most studies have identified only seeds in cheek pouches or in traps (Sánchez-Cordero & Fleming 1993 IN: BIOLOGY OF HETEROMYIDAE 596-617). However, in the rain forest of Rancho Grande, Venezuela, crab remains were found in the cheek pouches of Heteromys anomalus (Rood & Test 1966 AMER. MIDL. NAT. 79: 89-101) and in Guatemala and British Honduras, a beetle and some snails were also found in the cheek pouches of Heteromys desmarestianus (Murie 1935 MISC. PUBL. MUS. ZOOL. UNIV. MICHIGAN. 30 p), suggesting a possible predation. In this study we report on the possible use of snail species as food by Heteromys gaumeri in a subdeciduous tropical forest in the state of Yucatan, Mexico.

Heteromys gaumeri is endemic to the biotic province of the Yucatan Peninsula, Mexico. Very little is known about this species. There is a study about the general description of its biology and distribution (Schmidt et al. 1989 MAMM. SPEC. 345: 1-4), population fluctuation and reproductive pattern (Hernández-Betancourt 2003. PH.D. THESIS UAM-IZTAPALAPA), and its home range (Hernández-Betancourt et al. 2003 ACTA ZOOL. MEX. (N.S.) 90: 77-92).

This study was carried out in Hobonil Ranch, Tzucacab, Yucatan, Mexico, (20° 00' 06'' N - 89° 02' 30'' W). Climate is subhumid and seasonal with a wet and dry season and an annual precipitation range of 800-1200 mm. Annual average temperature varies between 22-26° C (INEGI 1989). The vegetation of the area is semi-deciduous tropical forest (Rzedowsky 1987 VEGETACIÓN DE MÉXICO 432 p).

We worked in two grids, one of 8100 m² with 120 Sherman traps set from March 1996 to April 1998 and another of 25600 m² with 162 traps set from January 2000 to December 2001. The distance between the rows and the columns was 20 m. Traps were baited with sunflower seeds. We used the mark-and-release technique during four nights per month. Captured animals were measured, marked by toe clipping and released. The snails found in cheek pouches and inside traps were collected and identified to the lowest possible taxonomic level (Burch 1962 HOW TO KNOW THE EASTERN LAND SNAILS. 215 p; Naranjo-García 2003 rev. Biol. Trop. 51 (Suppl. 3): 483 - 493).

We found that seven percent (n= 57) of the total population (n= 789) of H. gaumeri had snails in the cheek pouches or inside its traps. Fifty one percent of H. gaumeri were females and 49% were males. Eighty six percent were adults and 14% were juveniles. The snails found were choanopoma largillierti and c. gaigei (Annulariidae), Neocyclotus dysoni (Cyclophoridae) and Drymaeus shattucki (Bulimulidae). Choanopoma largillierti was found in both dry and rainy season. Choanopoma largillierti is commonly found in xeric and mesic vegetation but also can be found in agricultural habitats (Bequaert & Clench 1933 CARNEGIE INST. WASH. 431: 525-545, Bequaert & Clench 1936 CARNEGIE INST. WASH. 457:61-75). In contrast, C. gaigei was only found during the dry season. This species is common in mesic and submesic vegetation and not present in disturbed habitats. Neocyclotus dysoni was present in both seasons but was more frequently found during the rainy season probably because this species prefers humid forest (Thompson 1967 BIOL. SCI. 11: 221-256, Thompson 1969 ZOOLÓGICA 54: 35-77). Drymaeus shattucki was found during the 2000 dry season.

A significant relationship between the sex of H. gaumeri and seasonality was found (X²= 9.44, d. f. =1, p<0.01). The snails were found principally in the cheek pouches of females during the dry season and 35% of the sample of females were pregnant or post-lactating, while males and juveniles collected snails during the rainy season. Some of the snails found were dead with a complete or broken shell and some were alive with a broken shell. Six rats had two or three snails inside the traps and all others contained only one snail and only one individual had one N. dysoni inside the pouches.

Predation on invertebrates by Heteromys gaumeri had not been documented. We believe that the snails collected by the pregnant females could be food complement supplying water and proteins during reproduction season which occurs in the dry season (Hernández-Betancourt op. cit.), while males and juveniles probably fed on snails during the rainy season, because of the highest availability in the habitat in this period (personal observation). Future research on stomach contents, faecal analysis and the contents of H. gaumeri burrows needs to be conducted to provide information on the importance of snails in their diet.

Acknowledgments

This study was conducted with financial support of the Ministry for Public Education (SEP-México) PROMEP Programme as part of the PhD Dissertation of the senior author defended in the Universidad Autonóma Metropolitana (UAM), Mexico. We are grateful to Dr. Edna Naranjo from Instituto de Ciencias del Mar y Limnología-UNAM for provide training to the second author in the identification of snail species.