Reproductive and Spatial Ecology of Leptodactylus insularum (Anura, Leptodactylidae) in Panama
Tropical frogs show extensive variation in timing of breeding, reproductive strategies, and spatial patterns of calling males and nest sites. Over 2 yrs I studied a poorly known species of frog that exhibits maternal care. I report results from behavioral observations, breeding monitoring, and mark–recapture, describing the temporal and spatial distribution of males and foam nests in relation to pond depth and rainfall. I found that Leptodactylus insularum is a prolonged, episodic breeder with an average temporal lag of 12 d between breeding events. Although more nests were laid on nights following days with more rain, not every heavy rain triggered oviposition and there does not seem to be an absolute threshold in cubic millimeters of rain for laying eggs. Frogs laid their nests in shallow areas (15–115 mm) of the marsh and distributed nests in a spatially clumped pattern. Individual males were not recaptured in the same area of the marsh, which, combined with behavioral observations, suggests that they are not territorial. I recaptured 41% of 182 adult frogs tagged within a season, but did not recapture any adults across seasons, suggesting high mortality rates and a functionally semelparous life-history strategy. I found that juveniles reach sexual maturity in the following breeding season. I discuss the breeding strategies of L. insularum in relation to environmental factors and in comparison with related species and unrelated frogs with similar breeding patterns. Las ranas tropicales varían extensamente en cuanto a sus temporadas de cría, estrategias reproductivas, y patrones espaciales de sitios de canto en machos y colocación de nidos. Durante dos años, estudié una especie de rana poco conocida que provee cuidado maternal a sus renacuajos. Reporto resultados de observaciones de comportamiento, monitoreo reproductivo, y captura-recaptura, describiendo la distribución espacio-temporal de los machos y de los nidos de espuma en relación a la profundidad del estanque y la cantidad de lluvia. Encontré que Leptodactylus insularum muestra una estrategia reproductiva episódica y prolongada, con un periodo promedio de 12 días entre eventos de cría. Aunque las hembras pusieron más nidos en noches de días con más lluvia, no todas las lluvias fuertes incitaron oviposición y no parece haber un umbral absoluto en milímetros cúbicos de lluvia para que las hembras pongan huevos. Las ranas pusieron sus nidos en las áreas poco profundas (15–115 mm) del pantano y presentaron un patrón de distribución aglomerada. Las recapturas de cada macho no se concentraron en áreas particulares del pantano, lo que, combinado con observaciones comportamentales, sugiere que los machos no son territoriales. Recapturé el 41% de 182 ranas adultas marcadas en una misma temporada, pero no recapturé ningún adulto de una temporada reproductiva a la siguiente, lo que sugiere altas tazas de mortalidad y una historia de vida funcionalmente semélpara. Hallé que los juveniles alcanzan la madurez sexual en la siguiente temporada de cría. Discuto las estrategias reproductivas de L. insularum en relación a factores ambientales y en comparación a especies relacionadas, y además comparo mis resultados con estudios en ranas no relacionadas pero con patrones de cría similares.Abstract
Resumen
Reproduction in Leptodactylus insularum. (A) A male calling from a small depression in a flooded field. (B) A pair in amplexus. The male (above) is larger than the female and has hypertrophied arms (SVL: male = 95 mm; female = 79 mm). (C) An amplectant pair laying a foam nest. (D) A foam nest (ruler = 80 mm) laid on the water's surface, but hidden in vegetation. Note the developing embryos (black dots, <24 h old).
Daily rainfall patterns and timing of reproduction for L. insularum in Gamboa, Panama. The rainy season in 2008 started later and had less total rainfall than in 2006 or 2007. Shaded areas indicate the portions of the rainy season when fieldwork occurred. Open circles represent the nests laid in 24 h and closed circles represent nests laid on the consecutive night, i.e., in a 48-h period after a rainfall. Nests were monitored in Quarry Pond in 2006 and Kent's Marsh in 2007 and 2008.
The number of calling males and nests in Kent's Marsh relative to daily rainfall during the study periods in 2007–08. (A) More males called when there was more rain, but the response to rainfall was variable. Males did not call after every rainy day (see zeros at y = 0). (B) Similarly, more nests were laid on nights after more rainfall, but not every rain triggered reproduction.
Spatial distribution of males and nests in 2008. The locations of all males and nests in Kent's Marsh are shown over a map of average marsh depth (in centimeters). Morrow Blvd. is at the bottom of the map, and the hillside behind Kent's Marsh is at the top of the map. The positions throughout the season are pooled for all males, so that some males are represented more than once. Males were found spread throughout the shallow or dry regions of the marsh, and the nests were laid in clumped shallow areas along the water's edge. The darker regions indicate deeper water and the white areas indicate dry grass. Because Kent's Marsh is a flooded field, the perimeter of the marsh fluctuates with varying pond depths. When the marsh was deeper than average, the surface area of the marsh increased, and therefore the nests that seem to be laid on dry land (white regions) were actually laid over shallow water at the edge of the marsh.
Frequency histogram of the number of times an individual frog was captured within a season in 2007–08. The number of individuals captured is displayed on each column. Most (59.3%) frogs were only captured once, and only 16% of frogs were captured more than twice. Capture rate did not differ among males and females or across years.
The amount of time and distance in between subsequent recaptures in 2007–08. The positions throughout a season are pooled for all individuals, so that some individuals are represented more than once. Females attending nests or tadpoles (open circles) were present in the marsh more frequently (i.e., recaptured sooner) and closer to previous location than males (triangles) or females not providing care (filled circles). Three of the females that did not provide care were gravid, and returned later to breed. Males were spread out, and were not found in the same place or close in time.
