Do climate variables and human density affect Achatina fulica (Bowditch) (Gastropoda: Pulmonata) shell length, total weight and condition factor?

Abstract

The length-weight relationship and condition factor have been broadly investigated in snails to obtain the index of physical condition of populations and evaluate habitat quality. Herein, our goal was to describe the best predictors that explain Achatina fulica biometrical parameters and well being in a recently introduced population. From November 2001 to November 2002, monthly snail samples were collected in Lauro de Freitas City, Bahia, Brazil. Shell length and total weight were measured in the laboratory and the potential curve and condition factor were calculated. Five environmental variables were considered: temperature range, mean temperature, humidity, precipitation and human density. Multiple regressions were used to generate models including multiple predictors, via model selection approach, and then ranked with AIC criteria. Partial regressions were used to obtain the separated coefficients of determination of climate and human density models. A total of 1.460 individuals were collected, presenting a shell length range between 4.8 to 102.5 mm (mean: 42.18 mm). The relationship between total length and total weight revealed that Achatina fulica presented a negative allometric growth. Simple regression indicated that humidity has a significant influence on A. fulica total length and weight. Temperature range was the main variable that influenced the condition factor. Multiple regressions showed that climatic and human variables explain a small proportion of the variance in shell length and total weight, but may explain up to 55.7% of the condition factor variance. Consequently, we believe that the well being and biometric parameters of A. fulica can be influenced by climatic and human density factors.Keywords: Achatina fulica, alien species, gastropoda, condition factor, invasiveness species. Variáveis ambientais e humanas afetam o comprimento da concha, peso total e fator de condição de Achatina fulica (Gastropoda: Pulmonata)?Resumo A relação peso comprimento e o fator de condição têm sido bastante explorados em pesquisas envolvendo caracóis para obter o índice de condição física em populações e avaliar a condição do habitat. Neste trabalho, nosso objetivo foi descrever que variáveis influenciam os parâmteros biométricos e o bem estar de Achatina fulica em uma recente introdução. De novembro de 2001 a novembro de 2002, amostras mensais desses caracóis foram coletadas na cidade de Lauro de Freitas (Bahia), Brasil. Em seguida, os caracóis foram acondicionados em laboratório e foram obtidos o tamanho da concha e o seu peso. A partir desses dados a curva potencial e o fator de condição foram calculados. Cinco variáveis ambientais foram consideradas: amplitude de temperatura, temperatura média, humidade, precipitação e densidade humana. Regressões múltiplas foram usadas para gerar modelos preditivos através do critério de seleção e logo foram ordenados utilizando o critério de Akaíke. Regressões parciais foram usadas para obter os coeficientes de determinação do clima e fatores humanos. Um total de ...

Assessing Geographic Conchological Variations of the Different Banding Patterns in the Invasive Giant African Land Snail Achatina fulica From the Philippines

“…Considered as one of the "100 world's worst invasive species" [1]- [3] and the most ecologically damaging land snails [4], [5], the giant African land snail Achatina fulica is globally distributed in the places where the snail species multiply rapidly and may caused significant economic loose [6]. The broad distribution of the snails could not only be charged to active expansion from established populations but also to the repeated transportation opportunities provided by human [2], [7].…”

“…Studies that centered on the dispersal, distribution, and biology of the A. fulica have been performed since 1950s [6], [12]. However, information about the known factors affecting the snail biology, especially invasive species, is still lacking [13].…”

“…A. fulica in the Philippines shows conspicuous shell variations, which involve banding pattern, colour, size, and shape. Generally, shell shape and colour of land snails have been related to certain environmental conditions [6]. In the Philippines, it is notable morphological variation of shell shape of geographically isolated snails [17] and also a significant correlation of shell shape and banding pattern categorization [13] of A. fulica was observed using geometric morphometric analysis.…”

“…In the case of A. fulica, few studies reported that though the snail species exhibit wide environmental tolerance, the giant African snail preferred warm habitats [1], [2], [6]. In the study of [6], results of simple regression indicated that humidity had a significant influence on A. fulica total length and weight. Reference [11] stated that a smaller aperture is an adaptation minimizing the area of exposed surface, thus having the advantage by minimizing the loss of humidity under water stress conditions.…”

“…In the study on the littorine snail Bembicium vittatum [26] and on the phenotypic evolution of Candicula unifasciata [11], it was found out that shell shape correlated with physical habitat conditions. Furthermore, the A. fulica is a nocturnal snail and is moisture dependent, being more active in high humidity conditions [6], [27].…”