Side projects during PhD                    

                                                                                              Looking for glass frog clutches along a stream             A katydid eating an anole!  

Embryonic mortality and development in Hyalinobatrachium pulveratum (Anura: Centrolenidae) 

of southwestern Costa Rica

            Nearly all members of the neotropical family Centrolenidae are understudied.  I studied the population ecology of embryonic Hyalinobatrachium pulveratum along the Quebrada Bilingual in the Osa Peninsula, Costa Rica.  I used digital photography to regularly monitor development and to assess mortality of embryos in egg clutches.  Clutch size varied Nearly all members of the neotropical family Centrolenidae are understudied.  I studied the population ecology of embryonic Hyalinobatrachium pulveratum along the Quebrada Bilingual in the Osa Peninsula, Costa Rica.  I used digital photography to regularly monitor development and to assess mortality of embryos in egg clutches.  Clutch size varied from 23-57 eggs (mean = 42.3) and the duration of the embryonic period was 9-24 days (mean = 16.0).  In a subset of clutches, all embryos reached Gosner stages 23-25 within 11 d.  Forty-two percent of clutches hatched successfully with no embryo mortality.  Developmental failures caused the mortality of a small number of embryos in many clutches, whereas factors related to heavy precipitation caused high mortality in a small number of clutches.  Desiccation and predation also caused small amounts of mortality.  Overall, embryos in clutches with more than 10% mortality hatched earlier than embryos in clutches with less mortality, suggesting that the initiation of hatching is plastic.  These data provide the first field records of embryonic development and mortality for a formally little known species. 

Hawley, T. 2006. Embryonic mortality and development in Hyalinobatrachium pulveratum (Anura: Centrolenidae) of southwestern Costa Rica. Journal of Tropical Ecology 22:731-734.


 Different types of mortality in Hyalinobatrachium pulveratum egg masses from the Osa Peninsula, Costa Rica: clockwise from upper left, 1) normal clutch development except for one egg (white in colour) which is failing to develop either because it was not fertilized or it suffered from developmental abnormalities, 2) the same clutch as the upper left photo after presumed snake predation, note the clean removal of embryos with some jelly and other embryos remaining on the leaf,  3) desiccating embryos in the upper half of the clutch, evident from the irregular embryo shape, white colour, and thin jelly layer, 4) a clutch after insect predation, likely that of a katydid based on the opaque appearance of the jelly because of chewed yolk remains and irregular removal of embryos.

Similar projects on two other centrolenids: Hyalinobatrachium valeroii and Cochranella granulosa




amplectant pair of Hyalinobatrachium valeroii with clutches




Hyalinobatrachium pulveratum

Cochranella granulosa




Composition and ecological similarity of amphibian assemblages in modified habitats 

of the Canal Zone, Panama

            Despite the prevalence of exotic monocultures in neotropical landscapes, their impacts on local animal diversity are incompletely understood. Species residing in monocultures may be a nonrandom subset of the local fauna with phylogenetic or life history similarities.  Amphibian richness and abundance were quantified in teak (Tectona grandis), paja blanca (Saccharum spontaneum), and secondary forest habitats in the canal zone of Panamá.  Diurnal and nocturnal visual encounter and vocalization surveys were conducted along aquatic and terrestrial transects in each habitat.  To describe the microhabitat of each transect, temperature, relative humidity, and percent canopy cover were measured.  Eighteen species were encountered in the three habitats.  Transects in aquatic forest habitats had the greatest species richness, with 12 species from seven families.  In contrast, only four species from two families were encountered in the terrestrial teak and aquatic paja blanca habitats.  Members of the Leptodactylidae were dominant in the teak and paja blanca.  In addition, diurnally active species were absent from the monocultures.  Species richness was positively correlated with amount of canopy cover, low diurnal temperatures, and high relative humidity.  These results suggest that monocultures of teak and paja blanca support fewer species than secondary forest and that the species are a nonrandom subset of the local amphibian fauna.   

A teak plantation (to left) and paja blanca (to right), an invasive grass, within the Canal Zone of Panama