Numerous ant taxa naturally inhabit stems of live and dead Guadua bamboo (Bambusoidea, Poaceae) in western Amazonia. In an experiment at the onset of the wet season in Peru's Manu National Park, we augmented potential nest sites in stems of live bamboo, dead bamboo and dead caña brava (Gynerium sagittatum, another woody grass) at fi ve stations within each of ten bamboo patches and ten control areas outside those patches. Each experimental stem possessed three vacant and available internodes, pre-drilled with, respectively, large, small and linear holes, mimicking the range of forms of surveyed natural entrances. After 24 days, approximately 13 % of 798 available internodes had been colonized, the majority by fragments of existing colonies. Ignoring entrance type, which did not affect colonization for any species or species group, and censoring non-independent internodes of the same stem, we used individual stems as independent sample units in other tests. One specialist in live bamboo (Camponotus longipilis), and a likely specialist in dead bamboo (Camponotus depressus), were identifi ed based on overrepresentation in bamboo habitat and disproportionate occurrence in live or dead bamboo stems. A third species, Camponotus (Pseudocolobopsis sp.) was more abundant in bamboo areas but colonized both dead bamboo and dead caña. Relatively high abundance of standing dead stems in Guadua forests may account for the presence of a dead stem specialist. The experiment missed detecting specialization in one live culm specialist (Camponotus mirabilis), likely due to its failure to simulate conditions required for the species' unique modes of colony establishment and spread into new culms. Most opportunistic stem nesters colonized dead bamboo at signifi cantly greater rates than dead caña, but were either equally well represented in bamboo and control areas, or underrepresented in bamboo habitat. Given low colonization rates overall, underrepresentation in bamboo cannot be attributed to competition from bamboo specialists for nesting space. Rather, it may be due to combined effects of seasonal fl ooding of bamboo habitat, and greater importance of food limitation, relative to nest site limitation, in that habitat.

Camponotus mirabilis (Hymenoptera: Formicidae) is a highly specialized resident of live Guadua bamboo in western Amazonia. Workers in established colonies open and invade young, unlignified culms, and mature polydomous colonies occupy several‐to‐many adjacent stems. Multistoried carton shelves support brood inside culms, and larvae are nourished by honeydew of coccids (Cryptostigma guadua). Constructing a system of stem holes and wicks, C. mirabilis modifies occupied stems in ways that produce passive water evacuation. Nocturnally foraging workers gather both prey and wood fiber, a component of wicks. Diurnally, they boil aggressively from agitated stems, and are attacked by parasitic phorid flies (Diptera: Phoridae). Culms housing C. mirabilis are stouter and more erect than are unoccupied stems but are opened regularly by capuchin monkeys (Cebus apella) searching for brood and perhaps reproductive castes. Damaged by monkeys, weak‐walled Guadua stems frequently collapse and are abandoned by ants. Breakdown of brood shelves leaves nutrient‐rich carton suspended in water within basal internodes, but isotopic analyses fail to show that occupied culms utilize either nitrogen from carton or carbon respired by ants or decomposing debris. Lower foliar nitrogen concentration in occupied than in control stems suggests that coccids and ants parasitize host resources. A prior experimental survey of bamboo ants may have missed C. mirabilis because females found new colonies in culms occupied by another bamboo specialist, and established colonies invade only young bamboo growth.

Mensualmente, durante dos ciclos reproductivos consecutivos fueron colectados y estudiados ovarios de yamú Brycon siebenthalae en cautiverio, con el propósito de relacionar los cambios morfométricos y microscópicos y proponer la escala de maduración. El ovario fue un órgano sacular del tipo cistovario con ovogénesis sincrónica por grupos y desove total. Se diferenció en un ciclo anual de cinco fases de desarrollo de los ovocitos agrupados en dos grandes etapas: en la primera (de crecimiento primario o previtelogénico), hubo aumento del tamaño del núcleo, proliferación de nucléolos, visualización del corpúsculo de Balbiani, aparición de las envolturas de recubrimiento y aumento lento del tamaño celular. Los ovocitos en esta etapa se presentaron a lo largo de todo el ciclo y constituyeron el lote de reserva (ovocitos cromatina nucléolo y ovocitos perinucleolares). En la segunda etapa (de crecimiento secundario o vitelogénico), hubo engrosamiento de las envolturas foliculares y aumento rápido del tamaño celular por depósito de vitelo. Los ovocitos reclutados para esta etapa (del lote de reserva), constituyeron el lote de maduración y fueron los que ovularon en la siguiente reproducción (ovocitos alvéolo cortical, ovocitos vitelogénicos y ovocitos maduros). Se reconoció una fase de atresia folicular. La escala de maduración se definió en cuatro estadios: inmaduro o reposo, maduración, maduro y regresión o desovado.

Con el propósito de describir los cambios macroscópicos y microscópicos de los testículos y determinar la escala de maduración gonadal, cada mes durante dos ciclos reproductivos consecutivos, diez machos adultos de yamú (Brycon siebenthalae), criados en cautiverio, fueron colectados y sacrificados. Los testículos son órganos de estructura y funcionamiento tubular irrestricto. La espermatogénesis es cística y se presenta en seis fases: espermatogonia primaria libre, espermatogonia secundaria, espermatocito primario, espermatocito secundario, espermátide y espermatozoide. Cada túbulo seminífero contiene múltiples cistos y cada cisto células germinativas en una misma fase de desarrollo. La escala de maduración testicular comprende cuatro estadios: inmaduro o reposo, en maduración, maduro y regresión. El mayor valor de índice gonadosomático coincide con el mayor porcentaje de la fase y estadio maduro.