Ruth Madrigal-Brenes

In adult spiders, leg lengths vary within and between species and is associated with functions in web construction, sensory activities, and prey capture. However, little is known about how leg proportions change during ontogeny. Here we investigate whether leg length relative to body size is maintained throughout development in three cobweb spiders ( Latrodectus geometricus , L. mactans , and Steatoda grossa ). Because spiderlings of these species build webs and capture prey from the first instar, we predicted proportional growth across instars. We also evaluate which model (linear, quadratic, or Gompertz) best describes femur and tibia growth, and estimated growth rates (first derivative) and accelerations (second derivative) for each sex and species. Legs were proportionally shorter in early than in later instars in L. geometricus and S. grossa , whereas proportions remained similar across development in L. mactans . Femur and tibia growth was best described by a quadratic model in both sexes of L. geometricus and L. mactans , and in males of S. grossa . In contrast, females of S. grossa followed a Gompertz trajectory; with high early growth rates that declined toward maturity. Despite these differences in trajectories, leg segments showed similar magnitudes of acceleration within species. Across the three theridiid species, females showed two distinct ontogenetic patterns–steady increases in growth rate (quadratic) or rapid early growth followed by deceleration (Gompertz)–whereas males consistently followed quadratic trajectories. Conserved acceleration among leg segments may reflect developmental canalization that preserves functional proportionality during growth.

Habitat fragmentation and unplanned urban expansion increasingly threatens biodiversity, yet the genetic impacts on arthropods, and particularly spiders, remains understudied due to the lack of suitable molecular makers. Here, we used low-coverage genome sequencing and a bioinformatics pipeline to develop polymorphic microsatellite markers for Theridion evexum, a tropical spider with urban and natural populations. To increase the yield of DNA extracted from small spiders like T. evexum, we also optimized a Cetyltrimethylammonium bromide (CTAB) DNA extraction protocol. We sequenced eight individuals at 4X using paired-end sequencing on an Illumina Novaseq 6000. Reads were cleaned and processed using the Multi-individual Microsatellite Identification (MiMi) python pipeline. MiMi produced a total of 3999 putative microsatellites. After filtering for polymorphic loci with an allelic richness greater than three and present in at least 5 of the 8 sequenced individuals, 34 final markers were identified. An experimental validation of 13 of these 34 markers showed that 10 loci were polymorphic with at least three detectable alleles, one locus was monomorphic, and two loci did not produce PCR products. These markers will allow a better assessment of the effects of urban fragmentation and isolation across populations of this spider species. Furthermore, developing markers using low-coverage next-generation sequencing (NGS) and bioinformatic protocols provide a valuable approach for uncovering microsatellite markers at a reduced cost for other tropical species, thereby broadening the scope of molecular ecology research in the tropics.

Tropical montane forests are highly diverse ecosystems with high levels of endemism. Within these habitats, epiphytic plants are among the most diverse and understudied species groups. Despite their diverse reproductive and ecological traits, their influence on genetic diversity and fine-scale genetic structure (FSGS) has rarely been studied. We assessed how reproductive and ecological traits affect genetic diversity and FSGS within and among phoropytes in two epiphytic bromeliads: Aechmea mariae-reginae, a dioecious, hummingbird-pollinated, and bird-dispersed species, and Werauhia ampla, a hermaphroditic, self-compatible, bat-pollinated, and wind-dispersed species. We collected leaf tissue from 93 A. mariae-reginae and 94 W. ampla individuals. We used eight microsatellite loci to describe genetic diversity, structure, and FSGS in both species. Genetic diversity was higher in A. mariae-reginae than in W. ampla. Genetic diversity was not affected by multilocus identical genotypes. Both species showed low genetic structure among phorophytes. Significant FSGS was found in distance classes below 25 m in A. mariae-reginae, but no FSGS was found in W. ampla. The reproductive and breeding system of these species affects genetic diversity, with the dioecious and animal-pollinated species having higher diversity estimates. Limited seed dispersal by social birds in A. mariae-reginae results in significant FSGS within phorophytes. The absence of FSGS in W. ampla is due to extensive seed dispersal by wind.

Introduction: The interaction between plants and pollinators is vital for the reproduction of approximately 90% of angiosperms and directly affects ecosystems and agriculture. In tropical regions, 94% of plants require animal pollinators, and in Latin America, 58% of crops depend on pollination by insects. The stability and complexity of plant-pollinator interactions are influenced by several factors, such as floral morphology, which influences nectar accessibility and pollinator specialization. Objective: To compare the diversity and abundance of insect floral visitors in avocado, apple, plum, and blackberry crops in San Gerardo de Dota, Costa Rica. Methods: We systematically collected flower-visiting insects in these crops and identified them taxonomically to the lowest possible level. We then estimated alpha diversity for each crop and compared the community composition (beta diversity) of visiting insects among crops. Results: In 12 sampling visits, we collected a total of 2806 insects from 75 families across all four crops. Alpha diversity was greater in the avocado crop for all three indices (0D, 1D, and 2D). Apis mellifera was the most abundant species in all four crops, but Diptera was the most common group of visiting insects in avocado, particularly flies from the Syrphidae, Muscidae, Calliphoridae, Sarcophagidae, Sciaridae, and Tachinidae families. The insect community of the avocado crop was different from that of the apple, plum, and blackberry crops; however, the insect composition of the other crops was similar. Conclusions: The avocado crop is generalist in terms of floral visitors; this may be attributed to the size of the flower corolla, as flies with short mouthparts usually choose to feed on flowers with small corollas. Flowers of the other crops have similar morphology and are mainly visited by bees. The native entomofauna are abundant on the crop flowers, likely playing an important role as pollinators.

Introduction: Wild plants rely mainly on insects for pollination, and many of these plants are essential to maintaining a diverse and abundant community of crop insect-pollinators. In Costa Rican highland ecosystems, the diversity and abundance of insect floral visitors have been poorly studied, despite their importance and proximity to crops in this area. Objective: to determine the richness and composition of floral visitor insect species of native and ruderal herbaceous plants close to cultivated areas in San Gerardo de Dota, Costa Rica. Methods: We systematically collected flower-visiting insects along transects in two different sites and identified them to the lowest taxonomic level. We estimated alpha diversity for each season and 11 plant groups created specifically for this study. We defined these plant groups based on flower morphology, life history traits, and their taxonomic relatedness. We also compared the insect community composition across seasons and plant groups. Results: We collected a total of 1306 insects, mainly flies (Diptera), from 62 families on 46 plant species during 12 sampling visits. Insect diversity (alpha diversity) increased during the rainy season, possibly because resources (e.g., food and reproductive sites) for flies increase during this season. Insect species composition varied among plant groups. The most abundant insect communities overlapped extensively among plant groups, but other communities compose mainly by some tachinids, chloropids and wasps did not overlap between other plant groups. Conclusion: Seasonal differences in flower-visiting insects could be attributed to a greater availability of resources during the rainy season. Differences in the composition of visitor insects across plant groups were likely influenced by temporal variation in blooming of the different plant groups, blooming intensity, and flower traits. To preserve the rich diversity of floral visitors and the pollination services they provide, a diverse array of ruderal plants must be maintained.

Gene flow connects populations and is necessary to sustain effective population sizes, and genetic diversity. In the Lower Central American (LCA) region, the complex topographic and climatic history have produced a wide variety of habitats resulting in high biodiversity. Phylogeographic studies of plants from this area are scarce, and to date none have been conducted on palms. We used SSR and cpDNA markers to study the genetic diversity and structure of populations of the understory palm Chamaedorea tepejilote in Costa Rica. We found that populations of C. tepejilote have moderate to high nuclear (SSR) genetic diversity, likely due to large population sizes and its outcrossing mating system. Habitat loss and fragmentation may have contributed to increased genetic structure within slopes. High elevation mountain ranges appeared to be a significant barrier for gene flow among populations in the Caribbean and Pacific slopes, however, ranges are permeable through low elevation passes. In contrast, most populations had a single distinct cpDNA haplotype, supporting the hypothesis of several isolated populations that experienced decline that likely resulted in eroded cytoplasmic genetic diversity within populations. The haplotype network and Bayesian analysis linked populations in the Caribbean and the southern Pacific coast, suggesting that gene flow between Pacific and Caribbean populations may have occurred through the southern extreme of the Talamanca Mountain range in Panama, a colonization pathway not previously suggested for LCA plants. This is one of the first phylogeographic studies conducted on tropical palms in the LCA region and the first in the genus Chamaedorea, which sheds light on possible gene flow and dispersal patterns of C. tepejilote in Costa Rica. Our results also highlight the importance of mountain ranges on shaping gene flow patterns of neotropical plants.

Ecological traits and pollination mode associated with dioecious sexual expression in plants are likely to influence their reproductive success and levels of genetic diversity. Dioecy is an uncommon condition in Bromeliaceae. Currently, there is limited information on the reproductive ecology and genetics of dioecious and epiphytic bromeliads. Therefore, we studied the reproductive biology and genetic diversity of the epiphytic and dioecious bromeliad Aechmea mariae-reginae in Costa Rica. Flowering of pistillate and staminate plants in one population showed high synchrony and were pollinated by non-hermit hummingbirds. Sex ratio was biased to males (3.5:1). Fruit set was relatively high (68%) but there was high female reproductive variance (C. V. = 59.7%). The species is capable of parthenocarpic fruit production. Using eight nuclear microsatellite markers and six populations, we found moderate to high levels of genetic variation (HE = 0.571–0.726). Populations showed significant genetic structure (G'ST = 0.385) and Bayesian population assignment grouped them into lowland and montane clusters. Isolated montane populations had slightly lower genetic diversity probably due to lower effective population size caused by biased sex ratios and recent habitat fragmentation that limits long-distance pollinator movements and results in isolation by distance. If habitat fragmentation and isolation persist, populations in montane habitats may be at higher risk of decline and extinction.

In this paper, we describe the construction and function of the double sheet and tangle web of Tidarren sisyphoides (Walckenaer 1842). Web construction includes several stages: construction of the scaffolding that serves to support the rest of the web; filling in the dome-shaped and horizontal sheets; and construction of the upper tangle. During construction of the scaffolding, the spider descends by a pre-existing thread to the substrate, moves a few centimeters and attaches the dragline, then she ascends by the new thread, doubling the line or attaching it to another thread. The spider fills in the sheet while walking in an irregular pattern under the sheet, and attaching her dragline using either one or both legs IV simultaneously to hold pre-existing sheet lines against her spinnerets. During scaffolding construction and filling in the dome-shaped sheet, the spider returns frequently to the retreat, apparently using the same threads near the retreat each time. Threads of both the dome-shaped ...