Subterranean rodent – Argentina

Subterranean rodent – Argentina

Research project of area of action for Ctenomys mendocinus.

The tuco-tuco mendocino is a species of the genus that inhabits one of the most arid regions of Argentina

The equipment worked very well for the study of the home-range of these subterranean rodents. It allowed not only to know how tuco-tuco uses its space, but also its temporary dynamics. Collars were found even at 1.50 meters deep into the ground. The limited battery life of the collars used before finding Telenax had done, until now, impossible to harvest seasonal or annual data.

A subterranean rodent of drylands.

Paul A. Cuello, Leandro M. Alvarez and R. Ojeda.

Group of Biodiversity Research (GIB), IADIZA, CCT-CONICET-MENDOZA,. Av Ruiz Leal s / n. Cc 507, CP 5500 Mendoza, Argentina.  pcuello@mendoza-conicet.gob.ar

INTRODUCTION

Action Area

The action area is defined as an animal walking area for the development of all of its daily activities such as feeding, mating and caring for young (Burt, 1943). Also indicated is the area which is repeatedly passed by an animal. It is dynamics in terms of size and location (Skliba et al. 2008). Often the changes in the action areas, in size and position, are the result of individual strategies to maximize access to resources that limit their Fitness (Koprowski et al. 2007). Among the factors that may contribute to the dynamics of the action area highlights the availability of resources (Hubbs and Boonstra, 1998), the social and mating system (Fisher and Owens, 2000), population density and intensity of competition (Cutrera et al. 2010). Furthermore, in some cases the use of space by the animals is physically limited by their locomotive structures and means through which locomotion takes place. Subterranean rodents, an ecologically convergent group, are considered extreme cases. Most of its activities, such as feeding, mating and parental care take place in the subsurface environment (Nevo, 1979).

Although direct observation is a privileged way to understand the use of space and movement that an animal makes, it is impossible to achieve with underground animals. Given these limitations, radiotelemetry has been a fundamental tool for the study of the members of this group of mammals. The limited battery life of the collars used before finding Telenax had done, until now, impossible to harvest seasonal or annual data, and therefore there is little information on the seasonal dynamics in subterranean rodents.

Genus Ctenomys

In South America subterranean rodents are represented by the tuco-tuco (Ctenomys), these have the highest species diversity (60 species) among subterranean rodents. The geographical distribution of the genus is wide (between 17 ° and 54 ° south latitude) from southeastern Brazil to Tierra del Fuego (Rosi et al. 2001). Knowledge about the spatial organization in the genus is scarce and limited only to quantify the size of the areas of action, regardless of their spatial and / or temporal variations. For Ctenomys haigi the home-range of adults ranges between 35.5-38.9 m2, (Lacey et al. 1998) and C. talarum 34.91-70.10 m2, females and males respectively (Cutrera et al, 2006).

Ctenomys mendocinus  (tuco-tuco Mendocino) is a species of the genus that inhabits one of the most arid regions of Argentina, the Mount Desert (Figure 1). The species occupies grassland habitats, shrubs and Prosopis sp. Medium in size, with males being larger than females (Rosi et al. 2002). Estimates of the size and structure of the home range for this species are known only by digging their tunnel systems in piedmont and foothills environments (Rosi et al., 2000, 2002). In the lowlands and desert, only anecdotal data is all that is known about estimates of the size and structure of the home range by digging their tunnel systems (Contreras, 1980). The arid and semiarid environments, in which C. mendocinus inhabits, are characterized by extreme fluctuations in temperature, low rainfall and low availability of resources, these are extreme challenges that could significantly affect the space usage throughout the year.

Figure 1: Ctenomys mendocinus digging his tunnel. Photo: Daniela Rodriguez

Objective

Quantify the size of the action area of ​​male and female Ctenomys mendocinus.

Since the Telenax collars provided had a lifespan longer than 12 months it allowed us to begin studies on temporary changes to the action areas of Ctenomys mendocinus. The result of this analysis is being processed.

MATERIALS AND METHODS

Captures and Study Site: Action area and activity patterns in adult animals of tuco-tuco Mendocino were analyzed and quantified. The work took place from March 2009 to February 2010 in a protected area of ​​Mount Desert, Biosphere Reserve (MAB) Ñacuñán, Argentina (34 ° 02’S, 67 ° 58’W) (Figure 2). The study site was a zone of approximately 1 ha. in a forest dominated by mesquite (Prosopis flexuosa). The climate is semi-arid with a marked seasonality, where the summers are very hot and humid and cold dry winters. The average annual rainfall in the reserve is 328 mm, with a marked water deficit between the months of April to November All animals were caught using live traps, and these were specially designed and built to develop this study. For each animal gender, weight and external measurements were recorded.

Figure 2: Map of Argentina, in gray shows the extension of Mount Desert. The yellow box locates the Biosphere Reserve Ñacuñán, Mendoza Province, Argentina.

Telemetry:  Each animal was attached with a radio transmitter around the neck (TXB-009CL – Telenax, Mexico), which weighed approximately 4.7 g and accounted for 4.08% of the animal weight (SD 0.68%) on average (variation, 2.94 -4.70%) (Figure 3.A). The location of each of the transmitters, was recorded with the use of a RX-TLNX and a 3 element Yagi antenna (Telenax, Mexico) (Figure 3.B).

In the field, the position of each animal was recorded by the use of a Cartesian coordinate system (10 x 10 m.). The telemetry monitoring was distributed in different times of day and night, to obtain a sample as uniform as possible over 24 hours. Independent positions were recorded in animals, using a minimum of one hour interval, to prevent correlation between them. It was decided to adopt a method called “homing in”, that is to locate the animal being guided by the signal intensity of the radiocollar.

 Figure 3: There is a male Ctenomys mendocinus with collar on his neck.

Figure 4: Searching individuals, the antenna and receiver used are shown.

Statistical Analysis: We estimate the size of the home range using the two methods, 1) fixed kernel (Seaman and Powell 1996; Worton 1989) to obtain estimates of home range with 95% of the locations and 2) 100% minimum convex polygon (MPC ) for comparisons with published data from other subterranean rodents. Both methods were calculated using the package adehabitatHR (Calenge, 2011) software R 2.13.

To examine differences in the action areas of males and females we used Student’s t-test, if not complied with normality we used a Mann-Whitney rank-sum test performed R statistica 3 (citation).

RESULTS AND DISCUSSION

Captures: In total 15 animals were captured (8 males and 7 females). Males of C. mendocinus were significantly longer (240.64 ± 15.55 cm, t-test t = 2.51, P = 0.019) and heavier (131.79 ± 22.58 g, t-test t = 3.1, P = 0.004) than females (225.92 ± 7.14 cm ) and (108.75 ± 13.16 g), respectively. Animal tracking covered the 4 seasons, some of the animals did not complete the entire study because they were preyed by foxes.

Telemetry: Using all records of the year the average size of the action area with fixed Kernel method 95% for adult males was (144.72 ± 200.38. M2) and showed no significant difference with that of females (174.45 ± 233.26 m2 , t-test t = 1.18, P = 0.2370). Similarly, with regard to areas built with 100% MCP method also found no significant differences between sexes, males (36.28 ± 49.61 m2) and females (31.56 ± 47.04 m2, t-test t = -0.86, P = 0.3907) ( Figure 5).

Figure 5: Annual average size of the action areas of males and females measured with fixed Kernel method MCP 95% and 100%.

All analyzes performed in this work for the estimates of the areas of action and that the method used fixed kernel 95% and 100% MCP method, showed the same patterns. Males of C. mendocinus, body larger than females, should have larger areas of action. This is because by having greater energy needs larger areas should go to the meeting of enough food (McNab 1963). This is true in the case of Ctenomys talarum where males have larger areas of action and would be associated with larger body size (Cutrera, 2006). In our study we found no significant differences in the sizes of the areas of activity between males and females. The reason could be because females need to have areas large enough to offset the energy demands of pregnancy, breastfeeding and infant care. Especially considering that this cycle is consistent with the lowest availability in the year of herbs and grasses. Furthermore, the average size of the area of ​​action of C. mendocinus: 36.28-31.56 m2, estimated by radio telemetry and 100% MCP method is similar to those reported for other solitary subterranean rodents, Ctenomys talarum: 34.91-70.10 m2 (Cutrera, 2003); Ctenomys haigi: 35.5-38.9 m2 (Lacey et al. 1998); Spalax ehrenbergi: 63 m2 (Kushnirov et al. 1998).

Operation of the radio-telemetry.

The collars mostly had a life time of 12 months. Provided a detection range within about 20 or 25 meters, but although this range appears too short, it is because the antenna was cut in its entirety (only remaining the portion surrounding the neck of the animal), and on the other side the signal came from the underground. The antenna was cut antenna from the collar to not disturb the animals as they moved through the tunnels. Rodents move underground at depths of 30 cm on average, although we also found collars at 1.50 mtr. The location of individuals was very simple because the animals did not have great moves. The team worked very well for the study of the home-range of these subterranean rodents. And it allows not only to know how the tuco-tuco uses its space, but also to know their temporal dynamics.

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Article shared by Pablo A. Cuello.

Telenax wishes to thank Pablo, Leandro, R. Ojeda and CONICET-Mendoza for sharing this article.

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