Odonats del País Valencià: diversitat, factors implicats en la composició de les seues comunitats i respostes als senyals de risc durant la fase d'ou

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2017
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20-07-2017
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Abstract
Order Odonata is the group of insects chosen for the accomplishment of this doctoral thesis. Two diagnostic features highlights in this group. The copulating organ of adult males, located in the second abdominal segment; a feature which determines an exclusive reproductive behaviour: during mating the male bends the abdomen to reach the female genitalia. The other characteristic is the modification of the lower lip of the larvae, similar to an articulated arm, which is called as mask; this structure with hooks allows larvae to capture the food (Lorenzo Carballa & Cordero Rivera, 2012; Torralba-Burrial, 2015). Currently, odonates include the suborders Zygoptera, Anisoptera (both present in all continents except in Antarctica) and Anisozygoptera (present only in Asia) (Boudot & Kalkman, 2015), and approximately 6,000 species described throughout the World. They are ubiquitous in such opposing habitats as alpine lagoons and desert wadis (Riservato et al., 2009). But despite being a seemingly known group, many species remains uncatalogued, as patented with the discovery of new species of dragonflies for science around the world, allowing the update of inventories of both local and global odonates. In this sense, listing species makes also possible to implement conservation assessments and actions, as well as long temporary datasets, allowing the establishment of phylogenetic relationships, biogeographic assessments and the study of global phenomena such as climatic change. For these reasons, the objectives present in chapter 3 of the thesis are to update the Valencian odonates, to evaluate the biogeography of these different species and compare it with odonates of Catalonia and Aragon (two neighbour territories of the Valencian Country). Also, to discuss the current status of species that have not been found in the Valencian territory since the beginning of the 20th century, and to give potential explanations to the currently observed distribution in the Valencian species. Abundance and diversity are the key measures to understand how the communities of living organisms are structured. The first is limited to study the total number of individuals in a community, while the second one takes into account not only the number of individuals, but also the number of species (Morin, 2011). Among the different types of diversity defined by Whittaker (1960, 1972), alpha diversity corresponds to the diversity studied at a local community level, while beta diversity is the variation in the composition of species between different local communities. This implies different communities throughout space and time among places in a particular area. The interest to study beta diversity has increased in recent years (Juen & De Marco, 2011; Heino, 2011; Saulino et al., 2014; Wezel et al., 2014; Sueyoshi et al., 2016), and in the case of odonates there are many evidences that their communities are dynamic and suffer high rates of change throughout space and time. In fact, there are important recent findings about the structure of communities of odonates in Mediterranean systems and about the influence that these local and regional factors have on them (Soler Monzó, 2015). However, there are still many aspects to explore about the configuration of the Odonata communities and their implied phenomena and processes, about the combination of new methodologies for the analysis of these, and about how the impact of environmental factors on the beta diversity can be key in defining bioindicator species. For all the aforementioned, the objectives formulated for chapter 4 of this thesis are to determine the diversity and the factors responsible for the composition of the communities of adult dragonflies and damselflies in six transects of Valencian localities (Bicorb, Quesa , Sumacàrcer, Antella, Manuel and Alboi), all of them belonging to the basin of the Xúquer River. Also, to establish the relationships among Odonata species, type of landscape and physicochemical variables of water, and to identify potential bioindicator species. Dragonflies and damselflies have a complex life cycle in which the larval phase and the adult phase are of opposing habitats (aquatic and terrestrial, respectively). However, this separation of environments does not imply independence between the phases, since the environmental conditions in each one of them affect the later phases. Thus, the effects that are generated and that are transmitted through different phases are known as carryover effects. As explained by Stoks & Córdoba-Aguilar (2012), larval environmental conditions can affect, through carryover effects, the fitness of adults (at the level of size, flight performance or behaviour). This pattern can also be observed in the adult phase: the environmental conditions of adults can reduce longevity and fertility, which reduces the production of eggs throughout life, affecting the number of eggs and larvae of the next generation. Although the carryover effects from the adult stage to the offspring are quite unknown, it is known that they can affect the size of the egg or the selection of the oviposition zone. However, we are still far away to deeply understand the carryover effects in the egg stage, the most unknown stage of Odonata life cycle. Thus, in order to obtain a comprehensive approach to the life cycle, Stoks & Córdoba-Aguilar (2012) proposed to find how the environmental conditions imposed during the egg phase affect the fitness of the following vital phases of odonates. These animals have been considered as insects useful for devouring many other insects (Colomb, 1933) and it is known that they have great potential in pest control (Simaika & Samways, 2008). However, there is need to know about its beneficial role directly, as pest controllers, and indirectly, as disease controllers through the regulation of the vectors that transmit them. Taking this into account, the objectives set to chapter 5 of the thesis are to explore the antipredator responses at the level of egg stage, using Ischnura elegans (damselfly), and find the costs associated with these responses throughout the rest of the vital stages. Also, to explore the responses of eggs from Aedes albopictus (mosquito) to competitors and predators. In addition, to evaluate the existence of subsequent costs associated with these responses and to discuss the role of odonates as providers of the global vector regulation services of human diseases. Because the present thesis covers different odonatological fields and the objectives are configured in three blocks associated with specific chapters, the methodology associated with each one of them is as follows: - To achieve the objectives of chapter 3: Since the publication of the catalogue Les libèl·lules de la Comunitat Valenciana (Baixeras et al., 2006), the number of new appointments and new species has been increased, with the inventory registration of Banco de Datos de Biodiversidad de la Comunidad Valenciana (http://bdb.cma.gva.es/) and later publications. Therefore, in order to prepare all the knowledge related to odonates of the Valencian Country, a recompilation and evaluation of all odonatological findings has been carried out. Using this collection of information, the biogeography of Valencian dragonflies and damselflies has been analyzed according to the biogeographical elements of Torralba Burrial & Ocharan (2007b). In addition, our results are compared with those from Catalonia and Aragon. - To achieve the objectives of chapter 4: Sampling of adult odonates has been performed in the six transects mentioned, on sunny days and without wind (Sato & Riddiford, 2008), during spring and summer. Visual explorations of the Odonata composition have been made, and the number of individuals of each species has been recorded instantly to obtain abundance (Silva et al., 2010). Species identification has been done through books of Askew (2004) and Dijkstra & Lewington (2006), and Boudot & Kalkman (2015) has been used as the reference to the specific nomenclature. To obtain the landscape data, Google Earth images were used from the sampled areas, after being processed with the GIMP (GNU Image Manipulation Program) program. The physicochemical variables of water have been obtained from the Confederació Hidrogràfica del Xúquer. To establish relationships among species and environmental variables, several statistical methods have been used, mainly multivariate redundancy analyzes (RDA). - To achieve the objectives of chapter 5: The effect of risk chemical cues on the eggs of Ischnura elegans Mature females of Ischnura elegans have been captured and deposited one by one in plastic glasses. The walls of these have been covered with wet filter paper, which has served as oviposition support (Van Gossum et al., 2003; Stoks & De Block, 2011). The eggs of Ischnura elegans have been exposed to chemical cues from larvae of other damselflies. These larvae have been placed in glasses with water to emit chemical cues. To evaluate the effect of these on the eggs and their response to predation risk, treatment replicas have been established (in which the eggs have been exposed to the cues) and the corresponding control replicas (in which the eggs have not been exposed to the cues). Nauplii of Artemia salina and annelids of genus Tubifex have been used as food source (Sánchez-Guillén et al., 2005). When damselflies have reached the adult stage, sex has been determined, and the wings and dry weight have been measured, and subsequently have been compared between treatment and control. The effect of risk chemical cues on Aedes albopictus eggs Aedes albopictus females have been captured and deposited in containers with wet cardboard fibers, which in turn acted as oviposition support. In the same way as in the previous section, mosquito larvae have been placed in containers with water for the emission of chemicals. To evaluate the effect of these chemical cues on the eggs and their response to risk detection, treatment A replicas have been established (in which the eggs have been exposed to cues from Aedes albopictus larvae), treatment B replicas (in which the eggs have been exposed to cues from Ischnura elegans larvae) and the corresponding control replicas (in which this exposure has not existed). For the feeding of mosquito larvae, a mixture of bovine and tuna flour, yeast and vitamins (Puggioli et al., 2013) has been used. When mosquitoes have reached adulthood, sex has been determined, and the length of the wing and the length of the posterior tibia have been measured, which have been compared between treatments and control. Statistical analysis: R free software (http://www.r-project.org/) has been used. In general, these have been possible thanks to the use of different packages of R and they have consisted of different linear models, non-parametric correlations and multivariate analyzes. After the realization of specific methodology for each chapter, the main results and conclusions are: - From chapter 3: The record of 65 species of odonates in the Valencian Country is reported, which represent 82.28% respect to the 79 species of odonates registered in the Iberian Peninsula. Of the 65 species of Valencian odonates, the available records of Macromia splendens and Lindenia tetraphylla are old. Of these two species, it would be necessary to make exhaustive and consecutive planned searches to know if they are really present or not in this territory. In addition, the Lindenia tetraphylla specimens deposited in entomological collections and the information they provide highlights the importance of museums in providing data at the level of confirmation of presence and distribution of species. The contribution of citizen science to odonatology is also relevant, although some changes are needed to optimize the efforts of voluntary groups. The Valencian Country is enriched with odonates classified as Ethiopian elements, if we compare it with the territories of Catalonia and Aragon. This difference is probably due, in addition to the historical patterns of dispersion, to the greater geographic proximity and the climatic similarity with the African continent. Also, in a context of climate change and taking into account the issues of location and climate, it is probable that in the Valencian Country the number of Ethiopian elements will increase in the coming years. It is essential to continue the monitoring of the species of odonates to be aware of their real distribution in temporary series, in order to be able to empirically verify the effect of climate change and to improve existing biogeographic classification systems (or to create new ones). - From chapter 4: In 2011 samples were detected, in only six localities of the province of València (Alboi, Antella, Bicorb, Manuel, Quesa and Sumacàrcer), 29 species of odonates (almost 50% of the Valencian species). A clear negative effect has been found on the proportion of urban landscape that surrounds the sampled localities on the diversity of odonates. A positive effect of the surrounding urban landscape on the abundance of individuals has been found too, possibly due to high number of individuals of those species that are tolerant of anthropic activities. A positive correlation has been detected between the biochemical oxygen demand and the abundance of individuals, possibly resulting in a cascade effect from the high microbial activity associated with contamination to higher trophic levels. Through the different values of diversity and the different statistical analyzes employed (cluster, redundancy analysis (RDA) and principal response curve (PRC)), two groups of Odonata communities have been found in the area studied: one of the lowest zones of the river basin or "downstream" (Alboi, Antella and Manuel) and one of the highest or "upstream" zones (Bicorb, Quesa, Sumacàrcer). This distinction is linked to a gradient of anthropization, which is higher in the lower zones. Among the different relationships established between environmental variables (landscape or water) and particular Odonata species, the marked link between anthropized environmental conditions and Ischnura elegans, Platycnemis latipes, Erythromma lindenii and Trithemis annulata, agrees with the proposal of these odonates in adulthood as bioindicators of the human impact on the environment. - From chapter 5: Ischnura elegans eggs have hatched earlier in response to chemicals cues of predation risk from damselfly larvae of the Coenagrionidae family. It has also been noted that the individuals from eggs that have been under these cues have developed smaller wings. The hatching time of mosquito eggs Aedes albopictus has not been affected by the presence of chemicals cues of predation risk from Ischnura elegans larvae. However, the exposure Aedes albopictus eggs to these chemical cues affected the time of larval development based on sex. The results of the experiment suggest that the responses aimed at avoiding risks can be triggered during the egg phase and, although they may vary considerably between species, it is likely that they follow a generalized strategy in insects. Early warning responses can be particularly important in understanding insect ecology with some aquatic phase, some of which (like the Aedes albopictus mosquito) are global vectors of human diseases.
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