Climatic Cues Research Articles

Longest Insect Dormancy: Yucca Moth Larvae (Lepidoptera: Prodoxidae) Metamorphose After 20, 25, and 30 Years in Diapause

Fully grown larvae of Prodoxus y-inversus (Riley) undergo diapause in hardened cysts in the sterile tissue of Yucca baccata Torrey fruits. Dormancy normally lasts from early summer until the following May, but when optimal climatic cues, particularly winter chilling, are not received, the diapause is maintained. Larvae of the 1969 generation were collected in April 1970 in southern Nevada and held in winter conditions that varied but were warmer than those to which the population was adapted in Nevada. More than 180 individuals emerged synchronously following the 16th and 17th winters. Temperature data suggested that the intensity of winter chilling is the primary factor initiating diapause development and that after many years in diapause larvae are conditioned to respond to temperature regimes that were not acceptable for development in the early years of diapause. To test these hypotheses, larvae were held in constant warm temperatures for 4–5 yr, then exposed to a variety of winter conditions. Additional large groups eclosed following their 20th (151 adults) and 25th (125 adults) winters. X-rays before the 30th winter indicated that few larvae remained, and 14 moths emerged following 30 yr in diapause.

Induction of flowering in tropical trees by a 30-min reduction in photoperiod: evidence from field observations and herbarium specimens.

During the late rainy season in October 1997 we observed. over a range of >100 km, the highly synchronous emergence of flower buds in several deciduous tree species of the semi-deciduous tropical forest in Guanacaste, Costa Rica. Synchronous flowering soon after the rapid decline in day length around the September equinox and in the absence of any notable climatic cues suggested flower induction by declining photoperiod. By combining field observations and the analysis of flowering herbarium collections, we established highly synchronous flowering periods with low interannual and latitudinal variation predicted for photoperiodic flower induction for more than 25 tree species and a few herbs. We describe morphogenetic changes at the shoot apex of three species during flower induction and the suppression and induction of flowering in several herbaceous species by experimental daylight extension. The combined observations provide strong, mainly indirect evidence for photoperiodic induction of flowering in many tropical tree species. At low latitudes with annual variation in day length of 1 hour, flower induction must be caused by a decline in photoperiod of 30 min or less. This is the first report of photoperiodic control of flowering in trees.

Plant reproductive phenology over four years including an episode of general flowering in a lowland dipterocarp forest, Sarawak, Malaysia

The first systematic observation of a general flowering, a phenomenon unique to lowland mixed-dipterocarp forests in Southeast Asia, is presented. During general flowering, which occurs at irregular intervals of 3-10 yr, nearly all dipterocarp species together with species of other families come heavily into flower. We monitored reproductive phenology of 576 individual plants representing 305 species in 56 families in Sarawak, Malaysia. Observations continued for 53 mo from August 1992 and covered one episode of a general flowering cycle. Among 527 effective reproductive events during 43 mo, 57% were concentrated in the general flowering period (GFP) of 10 mo in 1996. We classified 257 species into flowering types based on timing and frequency of flowering. The most abundant type was "general flowering" (35%), which flowered only during GFP. The others were "supra-annual" (19%), "annual" (13%), and "sub-annual" (5%) types. General flowering type and temporal aggregation in reproductive events were commonly found among species in various categories of taxonomic groups, life forms, pollination systems, and fruit types. Possible causes for general flowering, such as promotion of pollination brought about by interspecific synchronization and paucity of climatic cues suitable for flowering trigger, are proposed, in addition to the predator satiation hypothesis of Janzen (1974).

Does irrigation affect leaf phenology in deciduous and evergreen trees of the savannas of northern Australia?

Abstract Soil moisture was augmented experimentally during two successive dry seasons and the intervening wet season in a humid tropical savanna in Darwin, northern Australia. Leaf phenology was monitored in four common tree species Termmalia ferdinandiana and Planchonia careya (both deciduous species), and Eucalyptus miniata and Eucalyptus tetrodonta (both evergreen species). Irrigation produced consistently significant effects in only T. ferdinandiana. In this species leaf‐flush was significantly earlier, canopy decline and leaf‐fall were significantly later and the attainment of full canopy was earlier in irrigated compared with non‐irrigated trees. Litterfall, and the seasonal patterns of contraction and expansion of stems (a measure of stem water status or storage) were not significantly affected by irrigation in any species. Leaf longevity in the deciduous species was 6–8 months; some eucalypt leaves lived for approximately 1 year, but none lived longer than 18 months. Irrigation had relatively little effect on leaf longevity. While variation in soil moisture is a potentially important cue to both leaf‐fall and leaf‐flush, stem water status and climatic factors such as vapour pressure deficit may also be important climatic cues to phenological behaviour.

Reproductive Cycles of the Talapoin Monkey (Miopithecus talapoin)

Reproductive cycles of female talapoins living in caged breeding groups were followed over 7 years, using visible changes of the perineum. Changes in the perineum during the extended adolescence of this species are described. There was a clearly defined breeding season, although its onset was not so abrupt as in the wild. During the summer months females show very small perineal swellings or none at all. Even during the breeding season all stages of the follicular phase of cycles are highly variable. Completed menstrual cycles are relatively rare since talapoins are highly fertile; they may be somewhat shorter than fertile cycles. Cyclical activity is modifiable by social stimuli, and it is suggested that differences in synchrony of breeding between wild and captive populations might be due both to indequate climate cues and to a lower level of social stimulation in captivity. The concept of the menstrual cycle had limited value in predicting reproductive activity in this highly fertile seasonal breeder.