ENSO episodes modify plant/terrestrial-herbivore interactions in a southwestern Atlantic salt marsh

Hemisphere scale events such as El Niño-Southern Oscillation (ENSO) can alter rainfall regimes worldwide, with important effects on species abundance and distribution. The evidence of ENSO effects on terrestrial communities is, however, restricted to a few ecosystem types. We explored the effects of ENSO episodes on plant/terrestrial-herbivore interactions through changes in the rainfall regime in a southwestern Atlantic salt marsh (Mar Chiquita coastal lagoon, Argentina. 37° 40′S, 57° 23′W). Surveys showed a positive relationship between winter rainfall and the abundance of the wild guinea pig Cavia aperea. The highest salt marsh abundances of C. aperea were associated with rainy periods during El Niño episodes, and the lowest ones were associated with the driest La Niña episodes. Rainfall was negatively associated with marsh sediment salinity, and experiments revealed that increased salinity reduces growth and increases mortality of cordgrass (Spartina densiflora). Salt increase also causes the highest percentage of dry area in S. densiflora leaves and reduced carbon content, and more salt content and secretion in S. densiflora stems. A factorial experiment in which we manipulated C. aperea presence and salinity along the edges of S. densiflora patches showed that plants can asexually invade unvegetated areas when salinity is reduced and C. aperea is excluded. Conversely, S. densiflora edges retracted when salinity was increased or there was C. aperea herbivory. Changes in nutritional quality of S. densiflora could explain the low herbivory of (and lack of impacts from) C. aperea in plots with high salinity. Thus, plant distribution responds directly to climate oscillations through changes in salt stress, and indirectly, through changes in plant-herbivore interactions. Herbivores respond indirectly to climate oscillations through changes in plant food quality, which suggests that top-down effects increase when bottom-up stressors are relaxed. ENSO events have direct and indirect effects on marsh communities that modulate the relative importance of top-down and bottom-up effects and have a considerable effect on the primary productivity of S. densiflora marshes.     

The influence of seasonality in estimating mangrove leaf chlorophyll-a content from hyperspectral data

Mangrove photosynthetic activity and, consequently, physiological stress can be monitored indirectly using leaf chlorophyll-a (Chla) measurements. Recent studies have demonstrated the feasibility of mangrove leaf Chla content estimation from in situ hyperspectral vegetation indices (VI) but no such research has been conducted using data collected from contrasting seasons (i.e. dry and rainy). In this study, mangrove leaves were collected in a sub-tropical forest of the Mexican Pacific for Chla content determination and in situ hyperspectral measurements (450–1,000 nm). Specifically, we tested 35 VI to estimate Chla content based on a leaf sample of 360 collected from the same trees during both the dry and rainy seasons. The forest examined contained three species of mangrove (Rhizophora mangle, Avicennia germinans and Laguncularia racemosa) exhibiting various conditions of health (dwarf condition, tall and healthy). A principal component analysis, followed by linear regression analyses, were conducted in order to identify those VI that best predict mangrove leaf Chla content during the two seasons. The results indicate that VI derived from hyperspectral measurements collected during the dry season are better at estimating leaf Chla content than those collected during the rainy season. Among the 35 VI, the Vog1 (R₇₄₀/R₇₂₀) index was found to be the best predictor of mangrove leaf Chla content, resulting in R ² values of 0.80 and 0.68 for the dry and rainy season respectively. These results would suggest that for identifying variation in mangrove forest stress (i.e. health) in sub-tropical regions, hyperspectral measurements should be carried out during the dry season.     

Climate change impact on neotropical social wasps

Establishing a direct link between climate change and fluctuations in animal populations through long-term monitoring is difficult given the paucity of baseline data. We hypothesized that social wasps are sensitive to climatic variations, and thus studied the impact of ENSO events on social wasp populations in French Guiana. We noted that during the 2000 La Niña year there was a 77.1% decrease in their nest abundance along ca. 5 km of forest edges, and that 70.5% of the species were no longer present. Two simultaneous 13-year surveys (1997–2009) confirmed the decrease in social wasps during La Niña years (2000 and 2006), while an increase occurred during the 2009 El Niño year. A 30-year weather survey showed that these phenomena corresponded to particularly high levels of rainfall, and that temperature, humidity and global solar radiation were correlated with rainfall. Using the Self-Organizing Map algorithm, we show that heavy rainfall during an entire rainy season has a negative impact on social wasps. Strong contrasts in rainfall between the dry season and the short rainy season exacerbate this effect. Social wasp populations never recovered to their pre-2000 levels. This is probably because these conditions occurred over four years; heavy rainfall during the major rainy seasons during four other years also had a detrimental effect. On the contrary, low levels of rainfall during the major rainy season in 2009 spurred an increase in social wasp populations. We conclude that recent climatic changes have likely resulted in fewer social wasp colonies because they have lowered the wasps'' resistance to parasitoids and pathogens. These results imply that Neotropical social wasps can be regarded as bio-indicators because they highlight the impact of climatic changes not yet perceptible in plants and other animals.     

垂叶榕榕小蜂群落及种间互作网络季节动态

群落中的物种相互作用构成了复杂的生态网络。有关物种的数量和组成的季节性动态变化已有较多的研究, 但是对于生态网络的动态变化知之甚少。揭示生态网络的动态变化对于理解群落的稳定性以及群落的动态变化过程和机理具有重要意义。本研究以垂叶榕(Ficus benjamina)榕小蜂群落为研究对象, 分别在西双版纳的干季和雨季采集了榕小蜂的种类和数量信息。比较了两个季节榕小蜂群落的动态变化以及共存网络的参数(例如网路直径、连接数、嵌套性和群落矩阵温度)变化。结果显示: 雨季榕果内传粉榕小蜂Eupristina koningsbergeri所占比例高于干季, 传粉榕小蜂的种群数量也高于干季, 而在干季非传粉榕小蜂的种类增加(干季15种小蜂, 雨季14种)。从榕树-传粉榕小蜂互利共生系统的适合度来看, 干季非传粉小蜂的增加对传粉榕小蜂和榕树的适合度是不利的。在干季, 共存网络物种间的连接数(干季0.95, 雨季0.47)多于雨季, 群落矩阵温度(干季23.24, 雨季2.64)也显著高于雨季。表明干季榕小蜂群落组成及种间关系较雨季更为复杂而多样, 高的矩阵温度暗示群落受到的干扰更大。     

Longitudinal changes in protistan bacterivory and bacterial production in two canyon-shaped reservoirs of different trophic status

The drastic interactions of weather as El Niño events with catchment and hydrological processes can cause unexpected changes in physical, chemical and biological properties of freshwater aquatic ecosystems. The severe drought during 1998–1999 in the northeastern region of Brazil induced ecological changes in numerous reservoirs as in Tapacurá reservoir, one of the biggest drinking-water suppliers in Pernambuco state. Investigations were based on monthly sampling over 2 years (May 1998–May 2000) conducted at 3 representative stations with 3 sampled depths through the water column (0.5 m, middle and 0.5 m above the bottom). Temporal changes in ecological processes, especially stratification, were driven by two major precipitation patterns, with an initial marked dry period (period 1) followed by a rainy season (period 2). Dissolved oxygen and pH variations, higher conductivity and alkalinity values, higher concentrations of particulate organic material (carbon, nitrogen and phosphorus) and higher levels of algal biomass (chlorophyll a) characterized the dry period (May 1998–May 1999). During this phase of low water level when the reservoir storage capacity reached a minimum of 3.9%, the concentrations of chlorophyll a gradually increased with a cyanobacterial bloom (Cylindrospermopsis raciborskii) noted in April 1999. The decline in chlorophyll a and particulate organic matter were observed as a result of the first rains in May–June 1999, with the drastic changes of quality of matter (higher particulate C/N ratio). After a phase characterized by the entire water column turning anoxic, a second phase in the stratification process could be identified from June 1999 with the pronounced rainfalls accompanied by an overturn event. Annual rainfall deficit and lack of reservoir water renewal in 1998–1999 linked to the 1997 El Niño consequences were important determinants of high eutrophication levels and drastic ecological modifications in Tapacurá reservoir.     

Breeding ecology of Kori Bustard Ardeotis kori strunthiunculus in the Serengeti National Park

The breeding ecology of the Kori Bustard Ardeotis kori strunthiunculus was studied in the plains of the Serengeti National Park, Tanzania in 2014 and 2015. Random transects were used to search for male courtship displays, nests, chicks and subadults. GPS satellite collars were used to locate nesting females. Linear regression analyses and post hoc tests were used to determine the predictors that contributed most to the variation of the dependent variables (courtship display, nest, chicks and subadults). The results indicate that courtship behaviour peaks during the short dry and short rainy season before the peaks in nests and chicks. The highest nest frequency was found in short grass habitats. Female Kori Bustard may undergo repeated nestings within a single breeding season. The adult sex ratio was female skewed during the breeding season. The Kori Bustard breeding season in the Serengeti plains is relatively long, lasting for almost nine months, and taking place during all seasons except for the long dry season. We recommend that management authorities conduct assessments of Kori Bustard recruitment as well as habitat suitability in the Serengeti ecosystem to develop future conservation strategies.     

Phytoplankton community structure and environment in the Kenyan waters of Lake Victoria

• 1 Phytoplankton species composition, numerical abundance, spatial distribution and total biomass measured as chlorophyll a concentration were studied in relation to environmental factors in September 1994 (dry season) and March 1995 (rainy season), respectively, in the Kenyan waters of Lake Victoria; 103 species were recorded.
• 2 Blue‐green algae (Cyanophyceae) were most diverse, followed by diatoms (Bacillariophyceae), green algae (Chlorophyceae) and dinoflagellates (Dinophyceae).
• 3 Twinspan separated the phytoplankton communities in the Nyanza Gulf and those in the open lake during both seasons. During the dry season, the Nyanza Gulf was strongly dominated by blue‐greens, while diatoms dominated in the open lake. During the rainy season, blue‐greens remained dominant in the Nyanza Gulf although the number of species found was lower than during the dry season; in the open lake, blue‐greens replaced diatoms as the dominant group and there were more species than in the dry season.
• 4 Canonical correspondence analysis indicated that the phytoplankton species distribution was significantly correlated with turbidity during the dry season and with SiO₂ during the rainy season. Chlorophyll a concentrations ranging from 2.0 to 71.5 mg m^‐3 in the dry season and 2.0–17.2 mg m^‐3 in the rainy season confirm earlier reports of increasing phytoplankton biomass in Lake Victoria since the 1960s.

     

Spatial distribution, size and density of nests of Myrmicaria opaciventris Emery (Formicidae, Myrmicinae)

Summary: We recorded over the course of one year the location of nests of Myrmicaria opaciventris on five sites in the region surrounding Yaoundé (Cameroon). On these sites, the colonies are polydomous and polygynous. The size of the largest colony, which was made up of 27 nests, was evaluated at 216,575 - 24,750 individuals of which 147,230 - 15,336 were workers. The nests are interconnected by trails that the workers dig during the rainy season. They consist of trenches that are slowly closed to form tunnels. Thanks to these tunnels, the workers are sheltered from their predators when going from one nest to another. They also have easy access to food sources far from the nests. We noted a seasonal variation in the location of the nests. It consists of a kind of budding. Depending on the case, the initial nest might survive or end up by being abandoned during the main rainy season or early in the dry season. The spatial distribution of the nests in the field is, in general, random and the density is lower during the dry season (from 6.2 to 26.4 nests/ha) than during the rainy season (from 12.1 to 50 nests/ha).     

Nitrogen enrichment during decomposition of mangrove leaf litter in an east African coastal lagoon (Kenya): Relative importance of biological nitrogen fixation

In situ decomposition of senescent leaves of twoabundant mangrove species (Rhizophora mucronataLamarck and Ceriops tagal (Perr) C.B. Rob),enrichment of nitrogen and activity of dinitrogenfixing bacteria during decomposition were investigatedduring both rainy and dry seasons in a tropicalcoastal lagoon (Gazi, Kenya). Rates of leafdecomposition were higher for R. mucronata thanfor C. tagal and were highest, for both species,during rainy season. Rates of decomposition, expressedas percentage dry mass loss, over a decompositionperiod of 50 days was: C. tagal (rainy season),69%; C. tagal (dry season), 27%; R.mucronata (rainy season), 98%; and R.mucronata (dry season), 48%. High rainfall anddiurnal tidal inundation appear to enhance the leafdecomposition process. Maximum rates of nitrogenfixation were 380 nmol N₂ h^-1 g^-1 dw forC. tagal (rainy season), 78 nmolN₂ h^-1 g^-1 dw for C. tagal (dryseason), 390 nmol N₂ h^-1 g^-1 dw for R. mucronata (rainy season) and 189 nmolN₂ h^-1 g^-1 dw for R. mucronata (dry season). Although N₂ fixation rates werehighest during rainy season, total nitrogenimmobilised in the leaves was highest during the dryseason. Biological nitrogen fixation can account forbetween 13 to 21% of the maximum nitrogen immobilisedin the decaying mangrove leaves. Nitrogen fixation, asa source of allochthonous nitrogen, sustains anitrogen input to the mangrove ecosystem, which addssignificantly to the nitrogen input through leaflitterfall.     

Environmental conditions modulate plasticity in the physiological responses of three plant species of the Neotropical savannah

Plasticity in plants could be changed due to abiotic factors, tending to increase fitness across environments. In the Neotropical savannah, a strong water deficit during the dry season is one of the main factors limiting the plasticity in physiological responses of plants. The present study aims to assess the plasticity in physiological responses and vegetative phenology of three plant species of the Neotropical savannah (Cerrado in Brazil) during the dry and the rainy seasons. The three species, Byrsonima verbascifolia, Roupala montana, and Solanum lycocarpum, occur in Serra do Cipó in the state of Minas Gerais, Brazil. The development and vegetative phenology of individuals of these three species were evaluated over the course of 1 year. In February 2012 (rainy season) and August 2012 (dry season), stomatal conductance (g _s), water potential (Ψ), photosynthetic quantum yield, and concentration of leaf photosynthetic pigments were measured. The relative distance among the physiological parameters of all individuals within each season was measured using the relative distance plasticity index. B. verbascifolia has pronounced senescence in July and lost leaves completely by the early September, while R. montana and S. lycocarpum have green leaves throughout the year. The three studied species had greater control of stomatal opening during the dry season. S. lycocarpum and R. montana had negative water potential values in the dry season and in the middle of the day in both seasons. In the dry season, the three species exhibited a decrease in F _v/F _m, with values between 0.7 and 0.75. The relative distance plasticity index varied from 0 to 1. R. montana demonstrated the greatest plasticity and S. lycocarpum had lower plasticity. Then, a seasonal effect on physiological response was observed in all three model-species, with lower values for leaf water potential and stomatal conductance, and increased photoinhibition, in the dry season. Ecophysiological traits, such as stomatal conductance and leaf water potential, exhibited the greatest plasticity. In addition, there was a seasonal effect on the plasticity in physiological responses of the three plants species of the Neotropical savannah. The results are contradicting the idea that water restriction in the dry season would reduce the plasticity in most species of the Neotropical savannah.     

Bionomic notes on Pachysomoides sp. (Hymenoptera: Ichneumonidae), a parasitoid of the Neotropical social wasp Polistes satan Bequaert (Hymenoptera: Vespidae)

Although most polistine wasp species are found in the Neotropical region, mainly in Brazil, only a very limited number of South American parasitoids or parasites are known to exist. We assessed the frequency of a hymenopterous parasitoid, Pachysomoides sp. (Ichneumonidae, Cryptinae), in the nests of the Brazilian independent‐founding wasp Polistes satan and compared the rates of the parasitization of P. satan by Pachysomoides sp. between the dry (winter) and wet (summer) seasons. Pachysomoides sp. larvae were seen to feed on P. satan pupa and were found in both the upper and lower parts of the host pupal cell (ca. 10 individuals in each host pupal cell). Approximately one‐third of the pupal cells in the P. satan colonies were parasitized in the dry season, whereas there were no parasitized pupal cells in the wet season. Consequently, the rates of parasitization by Pachysomoides sp. were significantly greater during the dry season than during the wet season due to unknown reasons.     

Influence of environmental,geographic, and seasonal variations in the chemical composition of Miconia species from Cerrado

Miconia albicans (Sw.) Triana and Miconia chamissois Naudin, commonly known as “pixirica” and “pixirica-açu”, two Melastomataceae species, are commonly found in Cerrado areas. M. albicans species grows in dry and humid habitats, so it has adapted to both conditions and M. chamissois species grows in humid environment only. In this work, we have investigated the content of triterpenes, flavonols and flavanones in three different Cerrado fragments of São Paulo State, involving distinct environments (dry and humid) and seasons (dry and rainy) to comprehend the complex interactions among plants and the seasonal, environmental conditions and geographic locations. The leaves plants materials were harvest in August 2016 (dry season) and November/December 2016 (rainy season) in Pirassununga, Pedregulho and Luíz Antônio in dry and humid environments. The contents of the standards rutin (R), quercetin (Q), miconioside B (B), matteucinol 7-O-β-apiofuranosyl(1 → 6)-β-glucopyranoside (matt), ursolic acid (AU), and oleanolic acid (AO) were determined by HPLC-DAD. The data were analyzed using nonparametric tests, Pearson's linear correlation, principal component analysis and hierarchical cluster analysis. The results demonstrated similar flavanone and triterpene production during the dry period, and similar flavonol and flavanone production in the rainy season, thus confirming a seasonal variation in the content of the compounds in the evaluated specimens. Our results also demonstrated intra- and inter-population variations in compounds patterns, M. albicans contained major amounts of the flavonols R and Q; their concentrations were higher in the rainy season. B and matt were the major compounds in M. chamissois; the matt concentration decreased in the rainy season. The triterpenes AU and AO occurred in both M. albicans and M. chamissois, but their production dropped during the rainy periods. Thus corroborating the adaptation of M. albicans and M. chamissonis to the high stress and low levels of resources presented in Cerrado.     

Phenology of Tree Species in Bolivian Dry Forests

Phenological characteristics of 453 individuals representing 39 tree species were investigated in two dry forests of the Lomerío region, Department of Santa Cruz, Bolivia. The leaf, flower, and fruit production of canopy and sub–canopy forest tree species were recorded monthly over a two–year period. Most canopy species lost their leaves during the dry season, whereas nearly all sub–canopy species retained their leaves. Peak leaf fall for canopy trees coincided with the peak of the dry season in July and August. Flushing of new leaves was complete by November in the early rainy season. Flowering and fruiting were bimodal, with a major peak occurring at the end of the dry season (August–October) and a minor peak during the rainy season (January). Fruit development was sufficiently long in this forest that fruiting peaks actually tended to precede flowering peaks by one month. A scarcity of fruit was observed in May, corresponding to the end of the rainy season. With the exception of figs (Ficus), most species had fairly synchronous fruit production. Most canopy trees had small, wind dispersed seeds or fruits that matured during the latter part of the dry season, whereas many sub–canopy tree species produced larger animal– or gravity–dispersed fruits that matured during the peak of the rainy season. Most species produced fruit annually. Lomerio received less rainfall than other tropical dry forests in which phenological studies have been conducted, but rainfall can be plentiful during the dry season in association with the passage of Antarctic cold fronts. Still, phenological patterns in Bolivian dry forests appear to be similar to those of other Neotropical dry forests.     

Succession of pelagic copepod species in coastal waters off northern Chile: the influence of the 1997–98 El Niño

A 2-year time series (17-d interval) of zooplankton, sampled from June 1996 through January 1998, along with oceanographic data, allowed the study of species abundances and diversity during non-El Niño and El Niño conditions at Mejillones (23° S), northern Chile. A total of 28 species was identified, of which the most abundant were the calanoids Paracalanus parvus, Calanus chilensis, Acartia tonsa, and Centropages brachiatus, the cyclopoid Oithona similis, and the poecilostomatoids Oncaea conifera and Corycaeus typicus. El Niño Southern Oscillation (El Niño) was first detected in the area in May 1997 and persisted until March 1998. We divided the time series into two parts: non-El Niño and El Niño conditions. The number of species significantly increased during El Niño conditions, but total abundance of copepods was greater during non-El Niño conditions. Although some expatriate species appeared during El Niño, such as the harpacticoid Microsetella norvegica and Eucalanus subtenuis, the diversity index of Hulburt was not significantly different between the two periods. Despite the dramatic alteration of oceanographic conditions during the El Niño period, we concluded that the community of pelagic copepods was not subject to drastic changes either in total abundance or in structure.     

“THE BIRDS OF SOUTH AFRICA”

Jones, P. J. 1980. The timing of wing moult in the Greyhooded Kingfisher in Nigeria. Ostrich 51:99-106.

The post-nuptial and post-juvenile moults of the Greyhooded Kingfisher Halcyon leucocephala took place in northern Nigeria between May and November (the rainy season) after migration from the southern breeding areas. Moult of individual birds lasted between 92 and 176 days, those starting moult latest (mostly juveniles) moulting fastest. This variation may be related to food availability during moult; those starting early do so before the rainy season begins in the north and before insect numbers increase, whereas those moulting later do so during the full flush of rainy season insect availability. This variability appears to be adaptive in allowing the complete moult to be fitted into the period remaining between the end of the breeding season, which is variable, and the southward migration in the early dry season, whose timing is relatively fixed.     

Contrasting demographies and persistence of rare annual plants in highly variable environments

Spatial and temporal variation in critical life history traits differ markedly between two co-occurring, rare and endangered annual plants, Gilia tenuiflora arenaria and Chorizanthe pungens pungens, that have restricted, but overlapping geographic distributions in coastal habitats of central California, USA. Environmental variation was extreme during the 6-year study (1997–2002), with the greatest differences between an intense wet, warm El Niño year (1998), followed by a very dry, cool La Niña (1999). Both species have similar increases in adult survival and seed set with wetter, warmer weather in spring, but they differed in other traits: more Gilia germinated in years with high rainfall and temperature, while more Chorizanthe germinated in dry, cooler years; Gilia abundance increased with the number of years since the previous large El Niño event, while Chorizanthe abundance declined; and Gilia abundance was independent of the previous year’s seed set, while Chorizanthe density was directly related to the previous year’s seed set. The strong negative associations of Chorizanthe abundance with warm, wet weather and with time since the previous El Niño probably reflect the particular sequence of annual weather patterns from 1997 through 2002, especially the extremes in 1998 and 1999. Since it germinates readily in most years under a wide range of winter conditions and does not develop a long-lived seed bank, Chorizanthe seedling abundance reflects recent additions and depletions of its seed bank, rather than prevailing weather, per se. In contrast, Gilia seeds may remain in the seed bank for many years, until relatively rare winter conditions trigger significant germination. These species-specific demographies enhance persistence and coexistence of these species, but the mechanisms differ from each other and from those described for annuals in other highly variable environments.     

Female reproductive cycles in two subspecies of the tropical lizard Mabuya striata

Summary Female reproductive cycles were examined in two subspecies of the live-bearing lizard Mabuya striata from Central Africa, an area with distinct rainy and dry seasons. The low altitude M. s. striata was reproductive throughout the year apart from a brief period at the start of the rainy season, and probably produced three clutches a year. Most females of the high altitude M. s. punctatissima were non-reproductive in the rainy season, came into reproductive condition in the early dry season, and gave birth in the late dry season. For some females, there was a second reproductive cycle starting in the late dry season with birth in the rainy season. For the low altitude M. s. striata it appears that availability of moisture may affect reproduction. For the high altitude M. s. punctatissima it appears that the low temperatures and short hours of sunshine of the early dry season constrain reproduction, and that reproductive cycles are timed to avoid birth occurring in the early dry season.     

Effects of El Niño-related Drought on Freshwater and Brackish-water Fishes in Suriname, South America

Droughts associated with the El Niño-Southern Oscillation (ENSO) affected fishes of brackish-water lagoons, freshwater swamps and a rainforest creek in Suriname, South America. The mean rainfall in the period August to February in 22 El Niño years was 76.6% of the mean rainfall in the same months of non-El Niño years. In the period 1900–1999, three out of four years in which an extreme drought (rainfall less then 60% of the mean value) occurred were El Niño years. The recent 1997/1998 ENSO event caused the second most severe drought in a 100-year record. Drying up of brackish-water lagoons, freshwater swamps and rainforest creeks was observed during El Niño-related droughts. In the lagoons ariid catfish died first, followed by snook, tilapia, mullet and tarpon, respectively. Landings of lagoon fish were positively correlated with rainfall in the period August–February. During the El Niño-related drought we observed failure of reproduction in three species of callichthyid armoured catfish in both coastal freshwater swamps and a rainforest creek in the interior. In the El Niño year 1997/1998, the no flow period of the rainforest creek was extended by four months beyond the long dry season and the dissolved oxygen levels in the dry-season pools dropped to 1.27mg O₂l^–1 (as compared to 4.53mg O₂l^–1 under running water conditions). Other fish species of the rainforest creek also showed decreased reproductive success in the El Niño year. We suggest that the stochastic effects of El Niño-related drought may be an important non-equilibrium component in the ecology of neotropical inland fish communities.     

Greater mycorrhizal colonization of unisexual morphs than of hermaphroditic morphs of Jacaratia mexicana during flowering and fruiting in central Mexico

Different sexual morphs of dimorphic and trimorphic populations of plants have different demands for resources correlating with phenotypic and ecological dissimilarities among morphs. Few studies have investigated the variations in mycorrhizal symbiosis across the sexual morphs of trimorphic plant populations. Here, we report seasonal variations in the mycorrhizal colonization of the roots of female, male and hermaphroditic trees of Jacaratia mexicana under field conditions in central Mexico. Mycorrhizal colonization was low in the rainy season, when J. mexicana bears only leaves, but high in the dry season when it flowers and fruits. In the dry season, the mycorrhizal colonization of female and male trees was over twofold higher than that of the hermaphroditic trees, and all three morphs had low mycorrhizal colonization in the rainy season. The lack of seasonal variation in the mycorrhizal colonization of hermaphroditic trees, together with other available evidence, supports the idea that hermaphroditic trees of J. mexicana might have some physiological disadvantages compared with male and female trees.     

Histology,ultrastructure, and seasonal variations in the bulbourethral gland of the African straw-colored fruit bat Eidolon helvum

We studied the morphological characteristics and seasonal changes of the bulbourethral gland of Eidolon helvum in a typical African tropical environment. Forty-eight bulbourethral glands were examined using gross anatomical, histological, histochemical, and ultrastructural techniques during the early rainy, late rainy, and peak dry seasons. The pear-shaped bilateral bulbourethral glands were located extra-abdominally in the inguinal region. Trabeculae from the capsule divided the parenchyma into numerous lobules of tubuloalveolar glandular acini. The mucosa was covered by a simple columnar epithelium consisting up of principal secretory cells, columnar dense cells and basal cells, which were progressively pronounced during the dry season. The principal cells contained eosinophilic granules, which were PAS positive while the dense cells did not show affinity for the stains. The mean gross weights, acini diameters, and epithelial heights were greater during the rainy season than the dry season. Ultrastructural evaluation showed that the cytoplasm of the principal cells contained well-developed Golgi complexes, rough endoplasmic reticulum, mitochondria, and secretory vesicles of varying electron densities and sizes. The secretory vesicles were numerous during the early rainy season, decreased during the late rainy season and were scanty during the peak dry season. The simple columnar epithelium observed during the rainy season was replaced by an undefined stratified epithelium during the dry season, and this was associated with cellular degenerations and regenerations. In conclusion, E. helvum has a typical mammalian bulbourethral gland, with a unique cell type, the dense cell whose functions are not well-understood. The gland exhibits cyclical seasonal variation in structure and secretory activity; being active during the early rainy season (breeding season), and showing the lowest activity during the dry season (non-breeding season). Glandular epithelial cell renewal occurs during the dry season in preparation for the next breeding season.