Bird migration times, climate change, and changing population sizes

Past studies of bird migration times have shown great variation in migratory responses to climate change. We used 33 years of bird capture data (1970–2002) from Manomet, Massachusetts to examine variation in spring migration times for 32 species of North American passerines. We found that changes in first arrival dates – the unit of observation used in most studies of bird migration times – often differ dramatically from changes in the mean arrival date of the migration cohort as a whole. In our study, the earliest recorded springtime arrival date for each species occurred 0.20 days later each decade. In contrast, the mean arrival dates for birds of each species occurred 0.78 days earlier each decade. The difference in the two trends was largely explained by declining migration cohort sizes, a factor not examined in many previous studies. We found that changes in migration cohort or population sizes may account for a substantial amount of the variation in previously documented changes in migration times. After controlling for changes in migration cohort size, we found that climate variables, migration distance, and date of migration explained portions of the variation in migratory changes over time. In particular, short-distance migrants appeared to respond to changes in temperature, while mid-distance migrants responded particularly strongly to changes in the Southern Oscillation Index. The migration times of long-distance migrants tended not to change over time. Our findings suggest that previously reported changes in migration times may need to be reinterpreted to incorporate changes in migration cohort sizes.     

Glandular Trichomes of Fagonia L. (Zygophyllaceae) Species: Structure, Development and Secreted Materials

The glandular trichomes ofFagoniaconsist of one secretory celland a multicellular stalk, which develops by division, elongationand elevation of epidermal cells. The latter become seperatedfrom the mesophyll and a subepidermal chamber is formed. Thelength of the stalk, which differs in the various species orvarieties is determined by the number of cell divisions and/or the extent of cell elongation. Although the basic morphologyand development of the trichomes of the species and varietiesexamined are similar, two types of mature trichomes can be distinguished:one occurs in the two examined varieties ofF. mollisand thesecond inF. glutinosaandF. arabica. The secretory cells of thesecond type possess a very thick wall and bear a porous cupuleon their top. Histochemical tests revealed that the sticky substancesecreted by the secretory cells contains mainly polysaccharidesand lipophilic compounds. The secreted material exhibits autofluorescence.InF. mollisvar.hispidachanges in the amount and shape of thefluorescent material inside the secretory cell, during the courseof development, have been observed. The contribution of theglandular trichomes inFagoniaspecies to survival in hot desertconditions is discussed. Fagonia; glandular trichomes; subepidermal chamber; secreted material; adaptation to desert conditions; stalk; fluorescence     

Translocation of 14C-Assimilates in Roses

Movement of ¹⁴C-assimilates from young and mature leaves to young rose shoots (Rosa hybrida cv. Marimba) was examined in two developmental stages. In the first stage after bud breaking the young shoot, especially its tip, depends for its supply of assimilates mainly on the mature foliage. At this stage young leaves are powerful sinks and retain 97% of their own photosynthates. The translocated 3% move mainly to the roots. At a later stage, just after the appearance of the flower bud, most of the leaves on the shoot become a source. The upper leaves supply assimilates to the flower bud and to the upper part of the stem. The ¹⁴C-assimilates from the lower leaves move in two directions, the larger part being directed downward.     

Factors affecting 14C-sucrose uptake by single-node explants of rose flower stems

Single node explants of ‘Baccara’ rose were fed through the basal cut surface with ¹⁴C-sucrose in agar. Accumulation of ¹⁴C-metabolites by buds is a steady process, while a quick uptake occurs in the stem piece during the initial stage of incubation suggesting a passive uptake at this stage. The uppermost 5-leaflet node buds had an initially higher ¹⁴C-uptake than the lowest bud. This difference disappeared after 2–3 days when growth started in both buds. Light enhanced uptake of ¹⁴C-sucrose by both stem pieces and buds. Accumulation of ¹⁴C-metabolites by buds was in direct relationship to buds deviation from the direction of gravity. This phenomenon was not evident in the stem part of the explant.