Spring bloom development of microbenthic algae and associated invertebrates in two reaches of a small lowland stream with contrasting sediment stability

SUMMARY. 1. Population growth rates and relative competitive abilities of the rotifer Keratella cochlearis f. tecta and the small-bodied cladoceran Daphnia ambigua were studied under different schedules of food addition but equal total food quantity (per 4-day interval). The initial population growth rate of Keratella was significantly affected by the feeding schedule and by the presence of competitors, while that of Daphnia was affected by neither factor. Population densities of both species tended to increase as the frequency of food addition increased.
2. Daphnia suppressed and excluded Keratella from mixed-species cultures when food was provided intermittently at a high concentration, but it failed to exclude the rotifer when food was provided in a near-continuous supply at low concentration. Keratella had only a minor suppressive effect on Daphnia in all mixed-species treatments.
3. Starvation experiments indicate that Daphnia is able to withstand food shortages for significantly longer periods of time than Keratella . These and other results indicate that the outcome of interspecific competition between these species may be influenced by me frequency and concentration at which food is supplied. Daphnia ambigua is competitively superior to K. cochlearis when food is concentrated or 'pulsed', but much less so when ambient food levels are chronically low. Patterns of food availability may have important effects in determining the relative abundance of rotifers and small cladocerans in natural zooplankton communities.     

A rare case of interspecific hybridization in the tracheophone suboscines: Chestnut-naped Antpitta Grallaria nuchalis × Chestnut-crowned Antpitta G. ruficapilla in a fragmented Andean landscape

Based on analyses of variation in plumage, morphometrics, vocalizations, and mitochondrial and nuclear DNA sequences, we document the occurrence of interspecific hybridization between a Chestnut-naped Antpitta Grallaria nuchalis and a Chestnut-crowned Antpitta G. ruficapilla in a high-elevation forest fragment in the Cordillera Central of the Andes of Colombia. One hybrid individual was collected and at least two were recorded singing. The hybrid specimen exhibits a combination of phenotypic traits that exclude other species of antpittas as potential parents, and its vocalizations combine elements of songs of both of its parental species. Genetic analyses demonstrate that the hybrid has G. nuchalis mitochondrial DNA and mixed nuclear DNA with copies corresponding to G. nuchalis and G. ruficapilla alleles, demonstrating that the female parent was G. nuchalis. Hybridization is considered extremely rare in most groups of suboscine passerines, but it may be facilitated when populations are decimated as a consequence of deforestation and habitat fragmentation.     

The larval head of Agathiphaga (Lepidoptera, Agathiphagidae) and the lepidopteran ground plan

Abstract. The larval head of Agathiphaga vitiensis is described. There is a complete hypostomal bridge but no hypostomal ridges. Adfrontal ridges and distinct ecdysial lines are absent. There are two vestigial stemmata (without lenses) on each side. The antenna is one-segmented. All ‘typical lepidopteran’ head setae have been identified. The corporotentorium is very slender; dorsal tentorial arms are present. Intrinsic labral muscles are lacking. The mandible has retained a tentorial muscle. The maxilla is without a discrete cardo and has but a single endite lobe; ‘intrinsic maxillary muscles’ and the ‘cranial flexor of the dististipes’ are lacking. The postlabium is undivided and without setae, the labial palp is one-segmented and the lateral prelabio-hypopharyngeal sclerotization is continued into an oral arm. Some of the ventral pharyngeal dilators arise on the tentorium; mouth-angle retractors and dorsal post-cerebral pharynx dilators are absent. The two brain lobes have almost parallel long axes and are united by a narrow (almost pure neuropile) bridge. The corpora cardiaca and callata are contiguous. The aorta is an open gutter in front of the retrocerebral complex. Available evidence on the ground plan structure of the lepidopteran larval head is reviewed. The ancestral head supposedly was prognathous and was autapomorphic in having the cranio-cardinal articulation far behind the mandible; it had a complete hypostomal bridge but neither hypostomal nor adfrontal ridges, its tentorium was probably stout and with dorsal arms. Paulus & Schmid (1978, Z. zool. Syst. EvolForsch. 16) described a lepidopteran/trichopteran synapomorphy in stemma structure. A tentative table of homologies between cranial setae in Lepidoptera and Trichoptera is presented; it differs considerably from the scheme of Williams & Wiggins (1981, Proc. 3rd Symp. Trichopt.). The mouth parts and their musculature must have been overall very primitive for a panorpid larva, but the number of maxillary palp segments was reduced (three). The ‘dististipes’sensu Hinton is considered to consist of complexly fused parts of the stipes and basal palp segments. The cephalic stomodaeum must have possessed all primitive groups of extrinsic muscles. The incomplete available information on Micropterigidae impedes reconstruction of some details of the lepidopteran ground plan. Larval head structures support the monophyly of an entity comprising the Agathiphagidae + Heterobathmiidae + Glossata. There is one suite of derived characters shared by Heterobathmiidae and Agathiphagidae only and another shared by Heterobathmiidae and the Glossata only; one of these must represent parallelisms.