The life cycle of three species of Portia (Salticidae, Spartaeinae).

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Theses / Dissertations
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Doctor of Philosophy
University of Canterbury. Zoology
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Hallas, Susan E. A.

The life cycle of the araneophagic, web-building, and therefore unusual salticid Portia (Spartaeinae) was investigated through laboratory studies of three species: P. fimbriata (Queensland, Australia), P. labiata (Sri Lanka) and P. schultzi (Kenya). The sequence and nature of morphological changes associated with the three stages of early post-embryonic development (prelarva 1, prelarva 2 and larva) were similar between the species. Several traits characteristic of active instars of typical salticids appeared in the larval stage of Portia, most notably prey consumption and silk spinning. Virtually the complete repertoire of the species-specific behaviours of Portia was present in first instars, including web-building, web-invasion, silk vibratory behaviours, and cryptic stalking. Leaf-raising behaviour appeared in instars 3-4, and in males disappeared, as did web-building. Five new grooming behaviours were described in Portia: palp chew; palp swipe; palp brush; leg chew; leg brush. The routes by which these and other behaviours may have become ritualised into silk vibratory and cryptic stalking behaviours were considered. Portia moulted every 2-3 weeks, maturing in instars 5-10 (varying between species, sexes, and individuals). The period of peak mortality varied between species but c. 24% of first instars of each species reached maturity. Adult female Portia lived two to three times longer than males (i.e., males had mean longevities of 61-172 days). The growth rates of Portia fluctuated during development (means: 0.24 lengthwise; 0.19 width wise), but always decreased in the final moult to maturity. Batch and egg sizes of Portia species varied with volumetric measures of female size (e.g., cubed body length, abdomen volume) and latitude of origin. Of the developmental traits of Portia, four were unusual for a salticid: precocial appearance of certain traits in the larval stage of post-embryonic development of Portia; moulting in a large three dimensional web rather than inside an enclosing silk nest; lengthwise growth rates comparable to those of web-builders of other families; and fluctuating rather than progressively increasing instar durations. None of these aberrant traits of the life cycle seem to clarify our understanding of Portia's position in salticid evolution. However, no traits of Portia's life cycle, typical or atypical, could not be explained by the Jackson and Blest hypothesis of salticid evolution.

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Copyright Susan E. A. Hallas